Name Alexandrite
Is a Variety of Chrysoberyl
Crystallography Orthorhombic
Refractive Index 1.745–1.759
Colors Varies in color with incident light: green, blue-green, or pale green in daylight; mauve, violet to red, purplish in incandescent light.
Luster Vitreous.
Hardness 8.5
Wearability Excellent
Fracture Weak conchoidal to uneven.
Specific Gravity 3.68–3.80
Birefringence 0.009–0.010
Cleavage Distinct to poor, 1 direction.
Dispersion 0.015
Heat Sensitivity Yes.
Luminescence Weak red in SW and LW.
Luminescence Present Yes
Luminescence Type Fluorescent, UV-Long, UV-Short
Special Care Instructions None
Transparency Opaque to transparent.
Absorption Spectrum Narrow doublet at 6805/6875, with weak, narrow lines at 6650, 6550, and 6490 and broad band at 6400-5550. Total absorption below 4700.
Phenomena Color change, chatoyancy (very rare).
Birthstone June
Formula BeAl2O4 + Cr
Pleochroism Deep red/orange-yellow/green. (Myanmar gems anomalous: purple/grass-green/blue-green).
Optics See “Identifying Characteristics” below. Biaxial (+), may also be (–), 2V = 70°.
Optic Sign Biaxial +, Biaxial –
Etymology Named after Czar Alexander II of Russia.
Occurrence Occurs in pegmatites, gneiss, mica schist, dolomitic marbles; also found as stream pebbles and detrital grains.
“Emerald by day, ruby by night,” alexandrite is well known for displaying one of the most remarkable color changes in the gem world. green in sunlight and red in incandescent light. However, the modern June birthstone is so rare and expensive few people have seen a natural alexandrite. This variety of gem-quality chrysoberyl makes an excellent jewelry stone. Alexandrites have two primary value drivers. First, the closer the colors to pure green and red, the higher the value. Second, the more distinct the color change, the higher the value. Alexandrites can exhibit everything from 100% to just 5% color change. Thus, the most valuable gems would have a 100% color shift from pure green to pure red. Blue-greens and purplish or brownish reds hold less value. Clarity also plays a significant role in grading. As is the case with a majority of gems, most naturally occurring alexandrite isn’t clean, facetable material. Most is best suited for cabbing. However, an alexandrite’s color change has more effect on its value than its clarity. For example, take two alexandrites of equal size. One gem is eye clean, with a 50% greenish blue to brownish-red color change. The other is an opaque cabochon with a 100% green to red color change. The opaque cab would be considered more valuable. Size always affects alexandrite value. You can see this reflected in our Price Guide below. In sizes up to one carat, top-quality natural gems can sell for up to $15,000 per carat. Over one carat, the prices range from $50,000 to $70,000 per carat! Alexandrite was discovered in the Ural Mountains of Russia in the 1830s. Noted mineralogist Nils Gustaf Nordenskiöld was the first to realize this unusual green, the color-changing gemstone was something new. In 1834, Count Lev Alekseevich Perovskii named the stone in honor of the then-future Czar of Russia, Alexander II. This connection to the Czars likely helped the gem gain prestige by association. In the 19th and early 20thcenturies, as historian David Cannadine notes, the Czars were widely considered the standard for royal pomp. (More recently, the British Royal Family has enjoyed this position). A combination of beauty, celebrity, and rarity helped create a mystique around this gem in the public imagination. By the 1950s, alexandrite joined the list of birthstones as the modern alternative to June’s traditional pearl.

How Rare is Alexandrite?

If not for alexandrite’s popular associations, the circumstances necessary for its formation, combined with its mining history, might have ensured the gem would be little known as well as extremely rare. To form, alexandrite requires both beryllium (Be), one of the rarest elements on Earth, and chromium (Cr). (Emerald also requires these two elements). However, Be and Cr rarely occurs in the same rocks or in geological conditions where they interact. Furthermore, the original source of alexandrites was almost exhausted after only a few decades of mining. Since the 1980s, more sources have emerged. Nevertheless, alexandrite remains one of the rarest gemstones.

Cat’s Eye Alexandrites

Cats Eye AlexandriteAlexandrite is a variety of the gem species chrysoberyl, well-known for its chatoyancy or “cat’s eye” effect when cabbed. As members of this species, alexandrites can also show a cat’s eye effect. However, such gems are quite rare.

Identifying Characteristics

Color Change

The color change gemstone phenomenon can occur under a variety of lighting types. When grading an alexandrite’s color change, gemologists consider the stone’s color in natural sunlight as the baseline. Thus, the classic alexandrite color change is green in sunlight and red in incandescent light. However, other types of lights can produce other colors, as shown below.
Alexandrite color changes - J Weyer.

Alexandrite color changes. Photo: J. Weyer.

Regional Variations in Alexandrites

Brazilian alexandrites tend to have pale colors, pale blue-green to pale mauve. However, finer gems have been found recently in limited quantity. Gemologists have detected substantial amounts (1,200 ppm) of the element gallium (Ga) replacing aluminum (Al) in some Brazilian materials.
Sri Lankan alexandrite often appears deep olive green in sunlight, whereas Russian stones appear bluish-green in the sunlight.
Zimbabwean gems show a fine, emerald-green color in sunlight but are usually tiny. If clean, they weigh under 1 carat. The color change in Zimbabwean gems is among the best known, but large, clean stones are virtually unobtainable from the rough from this locality. Other physical and optical properties of alexandrites vary according to their source.


A considerable market exists for lab-created alexandrite, first synthesized in the 1960s. Manufacturers can grow alexandrites through melt, hydrothermal, or flux methods. These synthetic stones have the same chemical and physical properties as natural alexandrites. They are real alexandrites but not natural. Although the synthetics cost far less than their natural counterparts, they still rank among the most expensive synthetic gemstones available. Gemologists can sometimes identify synthetic alexandrites by inclusions caused by various growth procedures. Melt techniques, like the Czochralski method, can create curved striae. Hydrothermal growth can create bubbles and liquid inclusions. Flux methods can leave inclusions of platinum or other seed materials. A considerable market also exists for lookalikes or simulants. These can range from synthetic corundum with alexandrite-like color change (produced very inexpensively) to actual, natural color-change chrysoberyl stones. Although alexandrite is a variety of chrysoberyl, not all color-change chrysoberyls are alexandrites. These gems also command a high price, but, again, not nearly as high as alexandrites. Buyer beware. If you find an alexandrite at a relatively bargain price, it’s likely not natural and possibly not an alexandrite. A professional gemological laboratory can make a determination.


Natural alexandrites usually don’t receive any treatments.


Mines in the Urals have re-opened but only produce a few carats of gem-quality material each year. In 1987, alexandrite was discovered in Brazil and later in Madagascar, Myanmar, Sri Lanka, and Zimbabwe. However, none of these sites produce as rich and vivid a color change as the original Russian source. The main source of large, natural alexandrite gems today is actually antique jewelry.

Stones Sizes

The largest known faceted alexandrite, a 65.7-ct green/red color change stone from Sri Lanka, resides at the Smithsonian Institution. The largest Russian gems weigh about 30 carats. However, the vast majority of alexandrites weigh under one carat. Stones over five carats are very rare, especially with good color change. Other alexandrites of notable size included in the following:
  • British Museum of Natural History (London): 43 and 27.5 cts (Sri Lanka).
  • Institute of Mines (St. Petersburg, Russia): a cluster of three crystals, 6 x 3 cm (Urals).
  • Fersman Museum (Moscow, Russia): crystal group, 25 x 15 cm, crystals up to 6 x 3 cm (Urals).
  • Private Collections: stones up to 50cts have been reported.


With a hardness of 8.5, alexandrite makes a very durable stone suitable for any jewelry setting. Nevertheless, take care when faceting the stone. Alexandrite is still sensitive to knocks and extreme heat. These gems have no special care requirements. You can clean them mechanically, per the instructions of the system used. Of course, you can also wash them with warm, soapy water and a brush.


Article Prepared by : සම්පත් සමරසේකර Sampath Samarasekara Chairman: Gemological Institute of Ceylon Chairman: Youth Gem Professionals Association Chairman: Sampath Gems Director: Ceylon Sapphire Gems and Jewels Director: Ceylon Gem Fair International Chairman: Nanosoft Web Develop Company Direct WhatsApp:

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blue sapphire



Name Sapphire
Is a Variety of Corundum
Varieties Color Change Sapphire, Padparadscha Sapphire, Star Sapphire
Crystallography Hexagonal (trigonal). Crystals common, often barrel-shaped, prisms with flat ends, sometimes bipyramidal; also massive, granular, in rolled pebbles.
Refractive Index 1.757-1.779
Colors All non-red corundum is considered sapphire. Colorless, white, gray, blue, blue-green, green, violet, purple, orange, yellow, yellow-green, brown, golden amber, peachy pink, pink, black. May show color zoning.
Luster Vitreous to adamantine
Polish Luster Vitreous to subadamantine
Fracture Luster Vitreous
Hardness 9
Wearability Excellent
Fracture Conchoidal. Frequent parting.
Specific Gravity 3.99–4.10; usually near 4.0
Birefringence 0.008-0.009
Cleavage None
Dispersion 0.018
Heat Sensitivity No
Luminescence See “Identifying Characteristics” below.
Luminescence Present Yes
Luminescence Type Fluorescent, UV-Long, UV-Short, X-ray Colors
Enhancements Heat treatment: common; diffusion treatment (placing a thin blue coating on colorless sapphire): occasional; irradiation (turns colorless gems yellow, orange, or light blue): rare.
Typical Treatments Heat Treatment, Infusion/Impregnation, Lattice Diffusion
Special Care Instructions None
Transparency Transparent to opaque
Absorption Spectrum See “Identifying Characteristics” below.
Phenomena Asterism, color change, chatoyancy.
Birthstone September
Formula Al2O3 + Fe, Ti, Cr, and other trace elements
Pleochroism Very pronounced.
  • Blue sapphire: intense violet-blue/blue-green
  • Green sapphire: intense green/yellow-green
  • Orange sapphire: yellow-brown or orange/colorless
  • Yellow sapphire: medium yellow/pale yellow
  • Purple sapphire: violet/orange
  • Brownish-orange sapphire: brownish-orange/greenish
  • Padparadscha sapphire: orange-yellow/yellowish orange
Optics RI: o = 1.757-1.770; e = 1.765-1.779 (usually 1.760, 1.768); Uniaxial (-).
Optic Sign Uniaxial –
Etymology From the Latin sapphirus for blue.
Occurrence Metamorphosed crystalline limestones and dolomites, as well as other metamorphic rock types such as gneiss and schist. Also, igneous rocks such as granite and nepheline syenite.
Inclusions See “Identifying Characteristics” below.


blue sapphire
A Rough Blue Sapphire 2.47ct from Rakwana, Ratnapura, Sri Lanka.Copyrighted Photo Credit: Sampath Samarasekara ( Chairman Gemological Institute of Ceylon )

All red, gem-quality corundum gems are considered rubies. All other colors of gem-quality corundum are considered sapphires. On the market, blue sapphires are usually simply called sapphires, while sapphires of other colors are commonly specified as yellow sapphires, pink sapphires, etc, and are collectively known as “fancy sapphires.” However, when discussing the physical and optical properties of sapphires, the term “sapphire” applies to all sapphires regardless of color. Sapphires get their extraordinary colors from trace elements such as iron, titanium, chromium, and others. Traces of vanadium may cause a color change in some sapphires. These sapphires show one color in daylight or fluorescent light and another in incandescent light.

sapphire crystals
Sapphire Crystals. Copyrighted Photo Credit: Sampath Samarasekara ( Chairman Gemological Institute of Ceylon )

Pink Sapphire or Ruby?

There is some disagreement about the distinction between pink sapphires and rubies. Some authorities classify only corundum gems with a dominant red hue as ruby. Others consider any red corundum, including pink, which is a light tone of red, to be ruby.

hot pink sapphire gemology
A Hotpink Sapphire from Embilipitiya, Ratnapura, Sri Lanka, Copyrighted Photo Credit: Sampath Samarasekara ( Chairman Gemological Institute of Ceylon )

What is a Padparadscha Sapphire?

Debates over colors and definitions extend to padparadscha sapphires, too.

Padparadscha Sapphire
An Orangish-Peach-Padparadscha Sapphire from Godakawela, Ratnapura, Sri Lanka, Copyrighted Photo Credit: Sampath Samarasekara ( Chairman Gemological Institute of Ceylon )

Subjective descriptions of these “lotus-colored” sapphires include “sunset,” “peach,” and “salmon.” The preferred color qualities range from light to medium-tone orange-pink to pink with a slight orange hue to orange with a slightly pinkish hue to a more deeply saturated orange-pink. These preferences also vary between consumers from Eastern and Western countries.

colors of sapphireThe Lore and Lure of Sapphires

For centuries, sapphire has been popularly associated with royalty and said to protect against poison and fraud. Star sapphires have also been associated with the power to divine the future. However, ancient references to sapphires may actually refer to lapis lazuli, another striking but gemologically distinct blue stone.

ancient blue sapphire earring
Gold earrings with pearls and blue sapphires, Byzantine Empire, 6th-7th century CE. Gift of J. Pierpont Morgan, 1917. Metropolitan Museum of Art, New York. Public Domain.
Identifying the actual gem species behind ancient gem names can prove challenging. Although the term “hyacinth” or “jacinth” is frequently associated with reddish or orange-brown varieties of gemstones like zircons and garnets, historically, the term also referred to blue gemstones. So-called hyacinths, such as the blue sapphires in these earrings, were popular in Byzantine jewelry.

Kashmir Sapphires

Kashmir Blue Sapphire
Kashmir Blue Sapphire

The most highly prized sapphires come from Kashmir. High in the Himalayas, these stones could only be found a few months out of the year. However, these sources are now exhausted. Kashmir sapphires are special. In addition to their fine color, what sets them apart from all others is their very fine silk inclusions.   These scatter light and give the stone a soft, velvety appearance. It creates a glow that, at the same time, minimizes extinction. This effect is only seen in one other stone: Myanmar ruby. Kashmir sapphires have a price structure all their own. Many sapphires are said to have “Kashmir color” or are called Kashmir due to their color. However, simply having fine color isn’t enough to prove its origin. Fortunately, Kashmir sapphires have a variety of features that make them easy to distinguish. Kashmir is the only place where tourmaline and corundum are found together. Although you’ll rarely see tourmaline inclusions in a finished sapphire, it often shows up on the rough or associated matrix.

Silk Inclusions

The most visible feature of Kashmir sapphires is their silk. It’s much finer than that seen in other sapphires. Its appearance is usually muted, rather than sharp and clear. This is what is known as being “velvety.” The first picture below shows the traditional fine, or velvety, silk as well as a “streamer” effect. (However, in this concentration, it will affect the clarity of the gem). In the second picture, the silk is much lighter but still soft in texture. Occasionally where the silk crosses, you’ll get “snowflakes” as seen in the third picture.

Left, traditional velvety silk inclusions. Center, lighter silk. Right, “snow flake” silk.

Left, traditional velvety silk inclusions. Center, lighter silk. Right, “snowflake” silk.

Silk can take on other distinctive appearances. The silk pattern in the picture below left is called “leather.” The sideways markings are what distinguish leather. The picture below right shows parallel streamers. When alone like this, they’re often called “comet tails.”

Left, leather silk pattern. Right, comet tail silk pattern

Left, leather silk pattern. Right, comet tail silk pattern.

Distinctive Kashmir Sapphire Features

While Kashmir stones have typical sapphire inclusions, they may also contain unique, elongated zircon crystals. Some of them are much more extreme in length than pictured here. These and other inclusions often have streamers.

Zircon crystal inclusions in Kashmir sapphires.

Zircon crystal inclusions in Kashmir sapphires.

Another identifying feature is extreme color zoning. You can usually see colorless bands between the blue. This feature alone wouldn’t be sufficient to make a positive identification, but in combination with any of the above features, it’s a strong indication.

Color zoning in Kashmir sapphires

Extreme color zoning in Kashmir sapphires.

Identifying Characteristics

Sapphires are highly prized jewelry stones. Determining their geographic origin and whether they’re natural or lab-grown is critical. Fortunately, examining their inclusions, luminescence, and absorption spectra can reveal clues.


Sapphires have some characteristic inclusions that can help distinguish them from other natural gems. See the section on corundum in our article on inclusions of specific gemstones. Inclusions can also help identify the source of sapphire.

hotpink sapphire

Hot pink, oval step-cut Sri Lankan sapphire, with a fingerprint (healed fracture) inclusion.

Some inclusions can also help identify a lab-made gem. For example, curved striae are found only in synthetic sapphires and rubies, never natural ones.

Star Sapphires

Sapphires can display asterism or the “star effect” due to rutile inclusions in their hexagonal crystal matrix. If this rutile is sufficiently abundant and precisely arranged, proper cabochon cutting can create six-rayed star sapphires.

star sapphire

Trapiche Sapphires

Trapiche Sapphire

Some sapphires can show a star-like “spoked wheel” pattern. However, these aren’t star sapphires.

Known as trapiche gems, these rare sapphires develop with carbonaceous inclusions between their crystal growth sectors, which look like the spokes of a wheel. Since sapphires have a highly symmetrical hexagonal crystal habit, trapiche sapphires can show six distinct spokes. Lapidaries can highlight the unusual appearance of these sapphires with slices or cabochon cuts. Trapiche emeralds are perhaps the best-known examples of these gems, but other types of gemstones can develop this pattern, including aquamarines, garnets, rubies, spinels, and tourmalines.


Natural Blue Sapphire Fluorescence

Typically, natural blue sapphires have no reaction to ultraviolet light (UV). However, there are some notable exceptions:

  • Some blue Thai sapphires fluoresce weak greenish-white in shortwave (SW) UV.
  • Sri Lankan blue sapphires may fluoresce red to orange in longwave (LW) UV and light blue in SW.
  • Blue color-change sapphires may show a weak, light red fluorescence in SW.
  • Some African blue sapphires may show moderate to strong orange fluorescence in SW.
  • Heat-treated blue gems sometimes fluoresce chalky green in SW.
Natural Fancy Sapphire Fluorescence
  • Green sapphires: inert.
  • Black sapphires: inert.
  • Sri Lankan yellow sapphires: fluoresce a distinctive apricot color in LW and X-rays, and weak yellow-orange in SW. The fluorescence in LW is proportional to the gem’s depth of color.
  • Pink sapphires: strong orange-red in LW, weaker color in SW.
  • Violet or alexandrite-like sapphires: strong red in LW, weak light red in SW.
  • Colorless sapphires: moderate light red-orange in LW.
  • Orange sapphires: a strong orange-red in the presence of LW.
  • Brown sapphires: usually inert or weak red in LW and SW.
  • Natural color-change sapphires: inert to strong red in LW, inert to moderate red to orange in SW.
Synthetic Sapphire Fluorescence

Some lab-created sapphires, both blue and fancy colors, can show different luminescent colors than their natural counterparts. This can help gemologists distinguish synthetics from mined gems.

  • Blue sapphires (synthetic): weak to moderate, chalky blue to yellow-green in SW.
  • Orange sapphires (synthetic): very weak, orange to red in SW.
  • Color change sapphires (synthetic): moderate orange to red in LW and SW, may fluoresce red in LW, and mottled blue in SW.
  • Brown sapphires (synthetic): inert to weak red in LW and SW.
  • Green sapphires (synthetic): weak orange in LW, dull, brownish-red in SW.
  • Pink sapphires (synthetic): moderate to strong red or orange/red in LW, moderate to strong reddish-purple in SW.
  • Violet sapphires (synthetic): strong red in LW, strong greenish-blue in SW.
  • Colorless sapphires (synthetic): inert to weak blueish white in SW.
  • Yellow sapphires (synthetic): very weak red in SW.

X-Ray Fluorescence

Some sapphires from Sri Lanka, Montana, and Kashmir glow dull red or yellow-orange when exposed to X-rays.

Sapphire Absorption Spectrum

The ferric iron spectrum dominates these stones. In green and blue-green gems, rich in iron, there are lines at 4710, 4600, and 4500 in the blue-green region. Also, lines at 4500 and 4600 may seem to merge and become a broad band. These three bands are generally known as the 4500 complex and are very distinctive in sapphires. Some blue Sri Lanka sapphires also show a 6935 red fluorescent line, and the 4500 line is very weak in these gems.

  • Lines have rarely seen in Kashmir sapphires. Heat-treated sapphires may show no lines or just at 4500.
  • Some flux-grown synthetic sapphires have a faint line at 4500, most not diagnostic.
  • Synthetic color change sapphires show line 4740.
  • Natural green sapphires show lines at 4500, 4600, and 4700.
  • Synthetic green sapphires show lines at 5300 and 6870.
  • Natural purple may show a combination of ruby and sapphire spectrum.
  • Natural yellow, Australian, 4500, 4600, and 4700.
  • Other natural yellow to orange-yellow not diagnostic.
  • Yellow and orange line sapphires, 6900, cutoff at 4600. If no iron lines, likely synthetic.
  • Orange, if only thin lines in red, the fluorescent line at 6900, and flawless, probably synthetic.

Synthetics and Simulants

Corundum gemstones, both rubies, and sapphires were first synthesized in the early 1900s by a simple flame fusion process. Today, many sapphires on the market are grown in labs. Gemologists need to be familiar with flame fusion as well as Czochralski, flux, and hydrothermal growth processes in order to distinguish natural from synthetic sapphires. Modern laboratory methods can simulate natural formation conditions so closely that colors and even inclusions look extremely natural. Such stones are difficult for all but the most highly skilled professionals to identify as synthetic. Due to the popularity of blue sapphires, other natural blue gemstones may be used to simulate their appearance. Glass, plastic, and other synthetic materials may also be used. Sometimes, they may be misidentified as sapphires, either accidentally or deliberately in order to sell them for higher prices. Although consumers may find some lookalikes difficult to spot, professional gemologists can usually distinguish these gemstones with standard tests. Although blue remains the most well-known and expensive sapphire color, you might also encounter simulated pink and padparadscha sapphires as their popularity increases. Cubic zirconia (CZ) can be manufactured colorless or in almost any color, so it can simulate not only diamonds but also many colored gemstones. The brilliant round-cut CZs in these sterling silver earrings imitate pink sapphires. Photo courtesy of and 3 Kings Auction.


There are numerous treatment methods for sapphires. For details on these processes and how to distinguish them, see our article on corundum treatments.

For decades, milky whitish sapphires from Sri Lanka known as geudas were heated at a high temperature to produce superb blue colors.


sapphire map Sapphires occur abundantly all over the world, but gem-quality sapphires occur much more rarely and in fewer locations. The following are some of the most notable gem sources. Consult our article on identifying the origins of rubies and sapphires for additional sources and information.

Sri Lanka

This ancient source still produces beautiful sapphires of all colors. Most blue sapphires on the market originate from here, too. These gems tend to show slightly grayish to violet-blue hues and have a light to medium tone.


Kashmir stones set the standard for evaluating blue sapphires. Verified historic Kashmir sapphires can sell for astronomical prices. They have a velvety texture and their colors tend towards slightly purplish blue, with strong to vivid saturation and medium to medium-dark tone. Review the section on Kashmir sapphires above for more information.


Australian sapphires tend to have dark colors, although some very fine gems have come from the area. Also of interest are the particolored sapphires which are usually yellow and green or yellow and blue.


Formerly known as Burma, Myanmar produces some very high-quality sapphires. The colors are slightly violet-blue, highly saturated, medium to medium-dark tone.


This nation produces blue sapphires abundantly. Their hue and saturation tend to be fine, although many are strongly dichroic, with a dirty green in one direction. Unless properly cut, the green will show in the finished stone. The stones are also very dark, requiring special cutting to show the color.



This American state produces sapphires of all colors. Unfortunately, most of them are “steely,” meaning they have grayish saturation. The sapphires from Yogo Gulch are an exception, with some of the world’s finest coloring. However, these small stones rarely finish over one carat.

Stone Sizes

910 ct large blue sapphire
910ct Rough Blue Sapphire found in Rakwana and trade by GIC Chairman Mr.Sampath Samarasekara. Copyrighted Photo Credit: Sampath Samarasekara ( Chairman Gemological Institute of Ceylon )
  • Smithsonian Institution (Washington, DC): 423 (blue, Sri Lanka, “Logan Sapphire”); 330 (blue star, Myanmar, “Star of Asia”); 316 (blue, Sri Lanka, “Star of Artaban”); 98.6 (deep blue, “Bismarck Sapphire”); 92.6 (yellow, Myanmar); 67 (black star, Thailand); 62 (black star, Australia); 42.2 (purple, Sri Lanka); 16.8 (green, Myanmar)
  • Private Collection: “Black Star of Queensland,” oval, found in 1948, 733 cts, world’s largest black star. A yellow crystal of 217.5 carats was found in Queensland, Australia in 1946.
  • Natural History Museum (Paris): the “Raspoli,” 135-ct brown sapphire, lozenge-shaped rough, clean.
  • Tested by the GIA: 5,600-ct sapphire cabochon; Montana blue sapphire, cushion-cut, 12.54 cts, believed largest stone from this locality.
  • Diamond Fund (Moscow): 258.8 (blue), fine, lively gem.
  • Royal Ontario Museum (Toronto, Ontario): 179.4 (golden yellow, Sri Lanka); 28.6 (Padparadscha, Sri Lanka); 43.95 (greenish yellow, Sri Lanka); 193.3 (blue star sapphire).
  • In 1929, the British mission to Burma (Myanmar) saw a 951-ct sapphire, which may be the largest ever found there.
  • American Museum of Natural History (New York): 536 (blue, “Star of India”); 116 (blue, “Midnight Star”); 100 (yellow, Sri Lanka); 100 (Padparadscha, very fine, Sri Lanka); 163 (blue, Sri Lanka); 34 (violet, Thailand).
  • Iranian Crown Jewels: Hollow rectangular cabochon of 191.6 carats; oval, yellow gem of 119 carats. Also fine Kashmir blue oval, nearly clean, 75 carats.

Not surprisingly, some sapphires have become well-known for their sizes as well as their histories. You can learn more about the Logan Sapphire, the Star of India, the Bismarck Sapphire, and other famous sapphires here.

Sapphire Trade Names

Please note: you may find these names used purely as descriptive terms. Sapphires can’t always be identified by their color alone. Always confirm the origin of sapphire with a vendor, especially if the gem is sold with a “geographic” name. Ask if the name refers to the actual origin or simply the color.

  • Adamantine spar: brown, usually opaque but may be translucent to transparent.
  • African: usually light in tone.
  • Australian: usually very dark, some yellow and green particolored.
  • Burma or Oriental: slightly violet-blue, highly saturated, medium to medium-dark tone.
  • Cashmere or Kashmir: velvety, slightly purplish blue, strong to vivid saturation, medium to medium-dark tone.
  • Ceylon or Sri Lanka: light to medium tone, slightly grayish to violetish blue.
  • Geuda: milky stones from Sri Lanka that can turn blue as well as yellow or orange when heated.
  • Montana: all colors, usually light to medium tone, grayish saturation.
  • Padparadscha: “lotus flower” color,” pinkish orange.
  • Thai or Siamese: dark blue.

Yellow sapphire is sometimes misleadingly referred to as “Oriental Topaz” or “King Topaz.” Green sapphire is sometimes misleadingly referred to as “Oriental Emerald.” Purple sapphire is sometimes misleadingly referred to as “Oriental Amethyst.” Since these sapphire colors are less well-known, vendors might try to present them as gems more commonly and strongly associated with yellow, green, or purple, for example. Consult our list of false or misleading gemstones names for more information.

Sapphire Care

Sapphire’s hardness is second only to diamond among natural gems. It also has no cleavage planes. This makes it a superb jewelry stone. Of course, a heavily included or fractured stone will be less stable. For reasonably clean stones, no special wear or care precautions are necessary. However, avoid cleaning any oil-treated sapphires with ultrasonic systems. Otherwise, you can clean sapphires with mechanical systems. Nevertheless, cleaning your sapphires at home with warm water, detergent, and a soft brush or taking them to a professional jeweler are your safest choices.

blue sapphire and diamond ring
Blue Sapphire and Diamonds 14 karat gold ring. Copyrighted Photo Credit: Sampath Samarasekara ( Chairman Gemological Institute of Ceylon )


Article Composed by : සම්පත් සමරසේකර Sampath Samarasekara Chairman: Gemological Institute of Ceylon Chairman: Youth Gem Professionals Association Chairman: Sampath Gems Director: Ceylon Sapphire Gems and Jewels Director: Ceylon Gem Fair International Chairman: Nanosoft Web Develop Company Direct WhatsApp:

Join with Gemological Institute of Ceylon for Practical Gemology Studies Facebook Page: Facebook Group: Facebook Profile: GI Ceylon

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blue sapphire 001 gemology

Gemstones Inclusions


Gemstones Inclusions

practical gemology check gemstones inclusions

By Phase Filing

Phase – Some of the substances with identical characteristics of physical state, chemical composition, and physical properties. Ex: two immiscible liquids inside the inclusion are described as two different phases, despite being both presented within the liquid state.

Single-phase inclusions

solid liquid gaseous inclusions
Single-phase inclusions: Solid – pyrite crystals in quartz; Liquid – thin films with interference colors in aquamarine, Gaseous – bubbles in the artificial glass, imitation of emerald.

Solid, Liquid, or Gaseous

Solid particles frequently contain single-phase inclusions (inclusions of other minerals or glass such as solidified melt from crystallization medium). Gaseous single-phase inclusions are found in a wide variety of natural and manmade glasses, as well as synthetic materials developed from a melt. Single-phase liquid inclusions are uncommon since fluid entrapment in a cavity is often caused by high pressure and temperature conditions. And when originally homogenous fluid is cooled to room temperature, it separates into two phases – liquid and gaseous – generating the relatively typical two-phase liquid-vapor inclusions.

Single-phase solid inclusions

This type of inclusion may be extremely widespread in nature. Such inclusions can be seen in the form of rutile or tourmaline needles in quartz, pyrite, or calcite crystals in emerald, zircon, or apatite in sapphire, olivine or garnet in diamond, and so on. They have simply captured crystals of other minerals within the host crystal. They can form prior to, along with, or after the crystallization of the host mineral. Occasionally, such inclusions are properly formed and represent a collectible object. They will be common or uncommon, and they will provide color or special optical phenomena to the stones. We can mention instances where multiple different minerals are stuck together as inclusions within a crystal. A crystal forming in a metamorphic deposit, for example, may trap a portion of the host rock composed of multiple minerals. Each mineral corresponds to a different solid phase in such circumstances, and hence such inclusions cannot be regarded as single-phase solid inclusions. They are classified as two-phase, three-phase, or multi-phase inclusions, depending on the number of different minerals comprising the aggregate.
hollandite inclusions quartz madagascar
Hollandite star in quartz from Madagascar. Field of view 6 mm.
flux inclusions synthetic emerald
Solid inclusions in synthetic Russian flux-grown emerald, corresponding to solidified amorphous molybdenum and vanadium oxide flux used as a grown medium for synthesis. Field of view 1.5 mm.
glass heat treated ruby
Vitreous inclusions in heat-treated ruby. During heat treatment routinely performed on rubies and sapphires, flux substances are commonly used to provoke recrystallization of the host corundum in fractures, and their healing leads to significant clarity improvement of the gem. Field of view 3 mm.

Single-phase liquid inclusions

Liquid inclusions in a single phase are uncommon. While many minerals crystallize from homogeneous aqueous fluids, the temperature at which they form is significantly higher than the temperature at the Earth’s surface. Thus, primary homogeneous fluid typically separates into at least two phases – liquid and gaseous – resulting in the formation of water filled with a gas bubble. Inclusions of liquid are frequently observed in crystals formed at low temperatures and pressures in shallow deposits. Additionally, they can form as a result of the separation of larger inclusions due to recrystallization of the cavity’s interior surface, a phenomenon known as “necking down.” As a result, the gas bubble is frequently contained within only one of the resulting separated cavities, with the rest containing only the liquid phase. In studies of fluid inclusions, inclusions that have been necked down are unsuitable for microthermometric analysis because their thermodynamic properties no longer correspond to the primary entrapped fluid.
liquid interference films in aquamarine 1
Interference films in aquamarine. Very thin cavities with single-phase liquid filling, forming interference films in aquamarine from Brazil. The interference colors are only observed under a very specific orientation of the sample; they are caused by so-called thin-film interference, the same phenomenon that causes colors of a drop of gasoline on the water surface. Field of view 3.5 mm.
tourmaline trichite inclusions
Several single-phase liquid inclusions can be seen in this tourmaline. They are formed as a result of the necking down the process, responsible of the formation of “trichite” inclusions, typical for this gemstone. The central part of the large fluid inclusion and some others contain vapor bubbles, but some completely separated parts of the same originally united cavity are filled solely by liquid. Field of view 3 mm.

Single-phase gaseous inclusions

These are gas bubbles that are frequently observed in glasses or crystalline materials formed when melted substances solidify. In this case, the medium for solidification is gaseous, as are the inclusions trapped during the process. Gaseous inclusions have spherical and elongated rounded shapes. Gaseous inclusions are frequently found in natural glasses such as obsidian, moldavite, and Libyan glass. They are also characteristic of man-made materials such as synthetic glass and any melt-grown synthetic analogs of natural gems such as Verneuil ruby, sapphire, and others. The gaseous medium disallows the material from recrystallizing at the cavity borders, resulting in the formation of negative crystals or the necking down phenomenon characteristic of fluid inclusions. Rather than that, trapped gas bubbles remain perfectly round, making them easily recognizable. They can exist as isolated spheres or as galaxies of bubbles of varying sizes that form groups, clouds, or veils. Gaseous bubbles are also frequently observed in the rubies and sapphires filled with lead glass that have flooded the market since 2004. These stones, which gemologists currently classify as synthetic, are largely composed of lead glass that fills large fractures and cavities in very low-quality natural corundum. The glass is typically populated bubbled, which provides an easy way to identify such stones, in addition to a noticeable flash effect observed on the filled fractures. Gas bubbles are frequently visible in natural resins that have solidified to form copal or amber. Hardening occurs in this case not as a result of the transition from melt to solid-state via cooling, but as a result of the polymerization of natural resins over time, heat, and pressure produced by overlying sediments. Certain bubbles in amber may also contain a liquid phase, most likely water captured in the resin deposition process.
bubble in verneuil ruby
Elongated gas bubbles and curved growth lines in synthetic Verneuil ruby. Field of view 3 mm.
bubbles glass imitation emerald
Groups of gas bubbles in the artificial glass, imitation of emerald. Field of view 4.5 mm.
bubbles swirls moldavite inclusions
Bubbles and swirls as inclusions in natural moldavite from Czech Republic. Field of view 5 mm.
insect bubbles copal colombia
Insect inclusion and gas bubbles in copal from Colombia. Field of view 5 mm.
lead glass filled ruby bubbles flash effect
Gas bubbles and flash effect in lead-glass filled ruby. Field of view 4.5 mm.

Two-phase inclusions

Cavities within crystals filled with two distinct phases are referred to as two-phase inclusions. Although liquid-vapor inclusions are the most common type, other combinations such as two immiscible liquids such as water and liquid CO2 or water and liquid hydrocarbons (petroleum) are also possible. It is critical to emphasize that the majority of two-phase inclusions, as well as three- and multi-phase inclusions, were trapped during the crystallization process as a single-phase fluid that later separated into two or more phases upon cooling to room temperature. Additionally, solid phases are frequently caused by solution, resulting in the formation of a crystal of a so-called “daughter mineral” within the cavity. In general, all phases that are distinct from a primary homogeneous fluid trapped during crystal growth are referred to as “daughter phases.” These phases include liquid, solid, and gaseous phases that form inside the inclusion cavity as a result of cooling to observation conditions. When the fluid inclusion is heated, all daughter phases gradually fade away, restoring the original homogeneous fluid. The following sections describe various types of two-phase inclusions. Liquid-vapor inclusions in two phases This is, without a doubt, the most common type of fluid inclusion, occurring in a wide variety of minerals and gems. Numerous crystals are formed from aqueous fluids at temperatures much higher than those at which we observe them. When the sample is heated to what is known as the homogenization temperature, we observe only one phase, which corresponds to the primary fluid. The temperature of homogenization is proportional to the lowest temperature at which crystals form, providing valuable information for mineralogical studies. Not every two-phase inclusion begins as a homogeneous fluid. When natural boiling occurs during mineralization, liquid and vapor phases may coexist within the primary fluid. One frequent scenario that results in boiling is the opening of closed fractures and the resulting decrease in hydrostatic pressure within the system, which results in boiling without the need for additional heating. Additionally, decreasing pressure can result in faster crystal growth (and entrapment of various inclusions) because the solubility of numerous minerals increases as pressure decreases. These two-phase water-vapor inclusions are frequently large and can be observed with the naked eye. These samples, commercially referred to as “enhydro,” are extremely rare and valuable collectibles. Numerous quartz and amethyst specimens with large aqueous inclusions and moving bubbles originate in Brandberg, Namibia, but are also found in other deposits. Water is not always the liquid phase in this type of inclusion. In Sri Lankan sapphires, two-phase liquid-vapor CO2 inclusions are common, occasionally with some additional solid phases within equivalent cavities. Gently heating such inclusions to 31.1oC is sufficient to merge them into a liquid phase.
two phase fluid inclusions fluorite
Groups of two-phase liquid-vapor inclusions in fluorite from China. Field of view 3 mm.

Two-phase liquid-liquid inclusions

In this case, the inclusion cavity is filled with two immiscible liquids at room temperature. In the case of liquid-vapor inclusions, heating the sample causes homogenization of the two liquids into a single fluid, corresponding to the primary fluid present during crystallization. However, cooling two liquids to room temperature separates them into two distinct phases under standard observation conditions. Water and CO2 are the most frequently encountered immiscible liquid phase combinations, as are water and liquid hydrocarbons (petroleum). True primary liquid-liquid inclusions are uncommon due to the presence of a gaseous phase bubble within the same cavity. However, liquid-liquid inclusions can also form as a result of the “necking down” of larger liquid-liquid-vapor inclusions, which occurs when a primary large cavity is divided into two or more distinct cavities and the vapor phase bubble is isolated to at least one of them, leaving only two immiscible liquids in the remaining cavities. Necking down is a common feature of fluid inclusions of all types; it occurs as a result of the modification of the borders of a primary cavity, with the host crystal dissolving in some areas and dissolved material reprecipitating in others. It frequently forms more energy-efficient negative-crystal-shaped cavities with borders that correspond to the host crystal’s faces. This process, which results in the formation of negative crystal cavities, can also result in the complete separation of one part of a large inclusion from the other via a barrier of reprecipitated material.
Fluid inclusions in barite crystals Most of them are two phase liquid rich fluid
Fluid inclusions in barite crystals. Most of them are two-phase liquid-rich fluid inclusions (liquid + vapor, yellow arrows). (A) Possible primary fluid inclusions are randomly distributed and some secondary fluid inclusions. At the bottom, there is a three-phase fluid inclusion (red arrow). (B) Secondary trails of two-phase fluid inclusions. (C) Matrix (left) -barite crystal (right) interface, showing trails of secondary fluid inclusions cross-cutting the barite crystal. Note that the large fluid inclusion at the center is three-phase fluid inclusion (red arrow). (D) Trail of two-phase secondary fluid inclusions showing stretching. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Two-phase liquid-solid inclusions

Due to two distinct phenomena, a solid phase is frequently present within a fluid inclusion cavity: • Occasionally, a solid particle is entrapped during crystal growth (captured crystal). • When the trapped fluid is cooled to space temperature, chemical compounds dissolved within it precipitate. Only in the second case is the solid phase frequently referred to as a “daughter mineral,” as it forms as a result of precipitation of the trapped fluid. In contrast to daughter phases formed from homogeneous fluid after the system (inclusion cavity) was closed, any phase (solid, liquid, or vapor) incorporated in an inclusion during crystal growth and fluid entrapment is referred to as a captured phase. Tiny crystals of various protogenetic and/or syngenetic minerals are frequently suspended in the fluid during mineralization and thus become trapped inside inclusion cavities along with the fluid. Additionally, particles of these minerals are frequently deposited on the growing crystal’s surface and act as a barrier to crystal growth, resulting in the formation of fluid inclusions adjacent to solid inclusions. As a result, solid phases are frequently found within the fluid inclusion cavity as well, but they have captured minerals rather than daughter phases. Daughter minerals are formed by highly soluble compounds; they also occur as crystals in all primary inclusions of an equivalent assemblage (unless necking down took place). They are relatively small in comparison to the total volume of inclusions, and thus the relationship between liquid and solid phase volumes is consistent for all inclusions of an equivalent group. The inclusion’s heating will result in the dissolution of daughter minerals, while cooling will result in their precipitation, preserving the solid phase’s initial volume. By contrast, captured minerals are found in only a few fluid inclusions of the same group, they have a tendency to have partially dissolved irregular shapes, their volume is highly variable, they are extremely large in comparison to the volume of the fluid inclusion, and in many cases, they will completely overpass the fluid inclusion’s borders. Heating fluid inclusions to the temperature at which all other phases are homogenized will not dissolve captured crystals. True primary two-phase liquid-solid inclusions are uncommon because they are typically accompanied by a vapor bubble, resulting in a typical three-phase liquid-solid-vapor inclusion. Such inclusions are characteristic of Colombian emeralds, for example. Nonetheless, some two-phase solid-liquid inclusions can form as a result of the “necking down” phenomenon, as described previously in the section on two-phase liquid-liquid inclusions.
captured solid phase fluid inclusion
Captured solid particles (not daughter minerals!) inside liquid-vapor inclusion in emerald from the Urals, Russia.
Field of view 0.15 mm.
Two-phase water and pyrite (captured) inclusion in quartz from Asturias, Spain. Field of view 8 mm.

Two-phase solid-gaseous inclusions

When observed at room temperature, we see a solidified glass with gas bubbles; it is no longer a fluid inclusion, but it was at the time of entrapment. These inclusions are characteristic of synthetic materials crystallized using the flux method (emerald, ruby, sapphire, alexandrite, spinel). A molten substance (flux) is used as a solvent for the crystallization of the mineral’s components and as a medium for crystallization in this process. While portions of flux are liquid when trapped by the growing crystal, cooling to room temperature causes them to solidify and contract, forming a small vacuum bubble within each cavity. As a result, we observe inclusions that are similar to natural gems’ two-phase liquid-vapor inclusions. The same process occurs in some gemstones that have been treated. For example, in heat-treated corundum (rubies and sapphires), when heating is carried out in the presence of borax or other fluxing agents with the intention of “healing” natural crystal fractures. These substances melt, enter open fractures, and act as a solvent for the host crystal, resulting in its recrystallization and fissure “healing.” Naturally, some flux material is trapped within the fissures and, when cooled, forms solid inclusions with bubbles, in a way comparable to that described previously for flux synthetics. Indeed, the appearance of inclusion veils in heat-treated corundum is frequently very similar to that of flux-grown crystals. When emeralds are treated with artificial resins to fill their fractures and cavities, trapped gas bubbles can occasionally be seen, as in the image below, where solidified resin fills a large cavity formed by the dissolution of a mineral inclusion (pyrite or calcite), and a large bubble is frequently visible within the filling material. Finally, two-phase solid-gaseous inclusions can be formed through heat treatment and subsequent melting of solid inclusions within the gem. Rubies and sapphires can withstand extremely high temperatures during heat treatment. Corundum has a melting point of 2044oC and can be heated to 1800oC. When the melting point of minerals contained in heat-treated stones is less than the heating temperature, they will melt and, in some cases, decrepitate, forming circular halos of solidified glass. In other cases, melted and solidified material will remain contained within the initial solid inclusion’s equivalent cavity. In any case, two-phase solid-vapor inclusions of solidified glass with bubbles are frequently formed as a result.
altered inclusions heat treatment sapphire
Molten solid inclusion in natural heat-treated orange sapphire, resulting in glass inclusions with gas bubbles filling cavities of initial mineral inclusions. Field of view 5 mm.
artificial resin filling emerald
Artificial resin with gas bubble filling very large cavity in natural emerald from Colombia, as a result of treatment to improve the clarity of emerald. Field of view 5 mm. Photo Juan Cozar.
flux inclusion synthetic emerald
Two-phase solid-gaseous inclusion in Russian synthetic flux emerald. Field of view 0.15 mm.
glass gas bubble heat treated sapphire
Two-phase solid-gaseous inclusions in heat-treated green sapphire. Field of view 2 mm.
three phase inclusion ural emerald
three-phase inclusion with water, liquid CO2, and vapor phases in emerald from the Urals, Russia. Data of typical volume percentages of each phase, microthermometry data, P-T conditions, and fluid salinity are also shown in the figure. Field of view 0.15 mm.

Three-Phase Inclusions

Three-phase inclusions are typically formed when a homogeneous fluid trapped in a cavity cools to room temperature and separates into three distinct phases. The most common types of inclusions are liquid-solid-vapor and liquid-liquid-vapor inclusions, which contain two immiscible liquids. Naturally, captured phases can also exist in three-phase inclusions, as discussed in the section titled “Two-phase liquid-solid inclusions.” Gemologists are very familiar with three-phase liquid-solid-vapor inclusions as they are characteristic of Colombian emeralds. In this case, the primary fluid is saturated with sodium chloride, and when the emerald crystal is cooled to room temperature from the temperature at which it formed (290-360oC, according to Cheilletz et al., 1994), a cubic crystal of sodium chloride crystallizes within the inclusion cavity, a so-called “daughter mineral” precipitated from the solution trapped as fluid inclusion. Aqueous fluid also separates into two phases as a result of cooling – liquid and vapor phases, as described in the section on two-phase liquid-vapor inclusions. When such inclusions are heated, complete homogenization of all three phases is frequently observed as a result of the salt crystal dissolving and the vapor bubble fading away. There is another type of three-phase inclusion that is quite common: those that contain two immiscible liquid phases and a vapor bubble. Water and CO2 are the two immiscible liquids most frequently found in inclusions, but water and liquid carbon hydrates (petroleum) are also quite common. As with other types of fluid inclusions, the fluid is homogeneous at the time of entrapment but separates into three distinct phases upon cooling to room temperature. When heated to the homogenization temperature, a single-phase fluid similar to that trapped during crystal growth will be produced. UV light is frequently used to detect liquid petroleum contained in fluid inclusions. In comparison, liquid CO2, which is present in a large number of inclusions, is occasionally more difficult to examine. Because liquid CO2 has a lower density than water, it is always concentrated near the gas bubble, forming a new phase between water and vapor. If the amount of liquid CO2 is significant, a double rim can easily be seen around the gas bubble, sometimes in the shape of a crescent moon. In comparison, a trace of liquid CO2 is frequently difficult to observe; at times, it merely makes the rim between water and vapor appear thicker and more defined. Cooling such inclusions increases the amount of visible liquid CO2, whereas slight heating above 31.1Co always results in homogenization of the liquid and vapor CO2, converting the inclusion to a two-phase liquid-vapor type. Video footage of microthermometric study of fluid inclusion in emerald from the Urals, Russia.

Multi-phase inclusions

Multi-phase inclusions are any combination of inclusions that exhibit at least three distinct phases at room temperature. Such inclusions are extremely uncommon in nature. Several examples of this type of inclusion include the following: Inclusions containing multiple daughter mineral phases, as well as water and vapor bubbles. Two or more distinct dissolved compounds are precipitated from the trapped fluid within the inclusion cavity in this case. Two immiscible liquids are added to the mix, along with a solid phase and a gas bubble. For example, in many inclusions containing water and petroleum, solid carbon hydrates (bitumen particles) are frequently observed floating in the water alongside the gas bubble. multiphase petroleum inclusion quartz pakistan Multi-phase inclusion in quartz from Pakistan, with yellow petroleum, a small amount of water in the lower right part, solid bitumen particles, and vapor bubble. Field of view 7 mm.
multi phase inclusion quartz
Another example of multi-phase inclusion, also in quartz from Pakistan, with liquid petroleum, gas bubble, and two additional phases, probably both corresponding to solid hydrocarbons – black dots and needles forming a star. Field of view 4 mm.


Article Prepared by : සම්පත් සමරසේකර Sampath Samarasekara Chairman: Gemological Institute of Ceylon Chairman: Youth Gem Professionals Association Chairman: Sampath Gems Director: Ceylon Sapphire Gems and Jewels Director: Ceylon Gem Fair International Chairman: Nanosoft Web Develop Company Direct WhatsApp:

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color change sapphire gemology

Gemstone Optical Properties


Gemstone Optical Properties

color change sapphire gemology
A Color Change Sapphire from Embilipitiya , Ratnapura, Sri Lanka in daylight, Copyrighted Photo Credit: Sampath Samarasekara ( Chairman Gemological Institute of Ceylon )

Sometimes we predict that light may be a very simple thing. But light plays a really important role in identifying gemstones. Therefore, we’d like to identify the key principles of light then make it easier to spot a gemstone. It is a really important factor for cutting and polishing a gemstone with optimal brilliance and character.

Properties of light

Electromagnetic energy

electromagnetic spectrum Light is a component of the electromagnetic spectrum, one of the elemental forces of the universe.

It is present in significant quantities everywhere. Light energy travels in waves. The energies of the electromagnetic spectrum vary consistently with their wavelengths.

Some are short, some are long. The wavelength has nothing to try and do with the quantity of energy carried. The wavelength determines it.

All wavelengths can have high or low energies. Although in nature, all electromagnetic energy is actually constant, varying wavelengths have distinct characteristics. For example, radio waves and X-rays.

We see a very tiny part of the electromagnetic spectrum as light. In this section, we identify different wavelengths as colors. When we see all the wavelengths right away, we describe it as white light.

The color black is lack electromagnetic energy during this portion of the spectrum. Just beyond the section of the visible electromagnetic spectrum, we discover ultraviolet and infrared.

While humans can’t see these light frequencies some animals can see them. We can feel them, Ultraviolet can give us sunburn, and that we feel infrared as heat. Simply put, light is a form of energy.

One color varies from another by the length of the waves of energy coming at us. Please note, colors are how our brains interpret these wavelengths.

Color has no relevance outside of human experience.



Light travels at 186,282 miles per second within the vacuum of space. That’s fast. Although the speed of light doesn’t change perceptibly within the Earth’s atmosphere, it slows when it enters a dense medium like a crystal.

When light passes from one medium to a different one, it slows down and changes direction or bends. The property we call the refractive index (RI) measures what proportion it changes.

In gemology, the refractive index is the relationship between the speed of light in a gem to the speed of light in a vacuum. If a gem has an RI of 1.655, meaning that light travels 1.655 times faster through space than it does through the gem.

Fortunately, gemologists don’t have to be compelled to measure the speed of light. Instead, they measure RI with a refractometer.

The gem is placed on a special surface, and light is gone through it. This casts a shadow on a scale. Where the shadow line falls on the scale marks the RI. Much simpler than attempting to measure the speed of light, right?

Knowing a gem’s RI is one of the foremost important pieces of data you’ll get when identifying a stone. It relates to many of the topics discussed below.  

gemology refractometer


Usually, light disperses evenly in every direction. For example, if you light a candle within the middle of a room, the brightest area is close next to the candle.

The further far away from the candle, the less light there’s.

If you’ll follow one ray of light, you’d see that it spreads equally in every direction because it travels. When light passes through certain substances, it becomes polarized.

That means it’s sideways vibrations at right angles to each other. As normal light, it emanates in every direction. When polarized, light only moves in linear directions (at right angles).

Crystals frequently polarize light, which accounts for a few of the optical phenomena we see. It’s a very important clue for gem identification.

gemology polarized light

Refractive Index

ice in water

Have you ever noticed how ice cubes in a glass of water nearly disappear? If they have rough surfaces, you will see them, at first. Just like unpolished gems, the rough ice surfaces scatter light in numerous directions.

As the edges of the ice melt and become smooth, the ice cubes become invisible. Just a touch of their outlines, “air bubble inclusions, and cracks remain to inform you the ice is there. Now, we’re stepping into the center of gemology.

Water and ice have an equivalent RI. While we all know that light will bend when it passes from one medium to a distinct one, when both substances have an equivalent RI, speed, and direction don’t change.

No alteration of the speed or direction of sunshine takes place between the water and thus the ice. You can clearly see the air bubbles, though, since they have a distinct index of refraction.

The cracks also disturb or reflect light. They act as mirrors, scattering light. Hence, they show up plainly as they interfere with the free passage of light. We know the technical definition of refractive index: the relationship of the speed of light during a gem to the speed of light in a vacuum.

However, the sensible implications of this have much greater significance for gemology. You’ve surely seen how a straw in a glass of water appears to bend at the surface. The difference in RI between the air and the water causes this.

Understanding how this bending works and so the way much light bends when passing from air to gem is extremely important when cutting gems for brilliance.

Gemstone Inclusions and Refraction

Inside gems, mineral inclusions may act like straws and air bubbles within the water. If the inclusions are transparent, what quantity they stand out relates on to how much their RIs vary from the surrounding material. For example, if an amethyst contains small crystals of clear quartz, those inclusions would be “low relief,” nearly invisible. Clear quartz has an equivalent RI as amethyst. However, if the amethyst contains inclusions of a mineral with a really different RI, they might show up clearly, in “high relief.”

optical properties inclusions

Fractures and Refraction

Fractures in a gem also disrupt the flow of light. Gem cutters must carefully place facets to apply discipline to the internal flow of light. After all, this might increase the “eye appeal” of the gem. Fractures can disrupt this discipline and cause loss of brilliance and scintillation and, thus, reduce the value and desirability of the gem. Filling a fracture with a substance of the same RI as the gem can minimize its light-disruptive effect. Just as light can go through water, ice, and water again without bending, so can it freely go through several layers in a gem. Of course, provided all of them have a similar RI. Oiling and Refraction Gem cutters most typically use oil to fill fractures in gems. Mineral and vegetable oils have RIs near to the lower RI range of gems. Epoxy resins also are used. Filling gem fractures is an ancient and extremely low-tech procedure. Simply place the stones in oil and keep them warm until they absorb the oil. Since emeralds are nearly always fractured, they commonly undergo this procedure. Fracture filling can do wonders for a gem’’s appearance. However, these gems require special care. Subjecting these stones to hot and soapy water can remove the fillings and every one their optical benefits.

Selective Absorption

Selective Absorption When you see all the wavelengths of visible light directly, you perceive it because of the color white. If you’ll only see some of the color spectrum, you perceive a hue. However, the physics of light is a bit more complex. If you were to get rid of just a small amount of the white light spectrum, there would be amounts of several different hues left. When this happens, our eyes average the wavelengths together. We perceive these partial spectrums as one hue, although there are several wavelengths of light coming at us directly. When light enters a crystal, it absorbs some of the light. Thus, the light exiting the crystal isn’t any longer white. Instead, we see a hue. This process is named selective absorption. How Does Color from Selective Absorption Differ From Pigment? We add pigments to materials to provide or change colors, like dye to your clothes or food coloring to the icing. Selective absorption adds nothing to a crystal. Most crystals themselves are colorless. Only the light passing through them, the color we see, changes. For example, a streak test on most gems, like a natural emerald, will leave a colorless streak. Selective absorption produces that emerald green color, not pigments within the gem. Only a couple of gems will show a streak aside from colorless or white. Streaks show the color of a gem without selective absorption live. Therefore, it’s not one among the gemstone optical properties.

The Spectroscope

Spectroscope We can see the spectrum of light with an instrument called a spectroscope. It separates white light by wavelength. If you inspect sunlight through a spectroscope, you’d see all the colours of the rainbow nicely displayed. However, if you inspect the light coming out of a coloured gemstone, you’d see dark lines here and there. These are the areas of selective absorption. Selective absorption patterns are sometimes diagnostic. Thus, you’ll use them sometimes to differentiate one gem from another. To the right, you will see the absorption spectra of white light, ruby, and garnet as viewed through a spectroscope. white light has no dark lines. When held in your hand, rubies and garnets look very similar. Their spectrums vary considerably. While the garnet spectrum has just a few lines, the ruby spectrum has large areas of absorption also as several distinct lines. Although the spectroscope may be an important tool for gem identification, it does have limitations. Several gems share patterns. Take gems colored by the element chromium. The presence of chromium creates identical or very similar absorption patterns, whether it’s in a ruby, tourmaline, diopside, or other minerals. On some occasions, a spectroscope can make a critical distinction. Generally speaking, however, you’ll get more useful information from other instruments.

Color Change

color change gemstones While sunlight contains all the visible wavelengths of electromagnetic energy, other varieties of light don’t. They have peaks and valleys, rather than an even distribution of electromagnetic energy. For example, our electric lights appear white, but that’s a result of our eyes averaging the wavelengths together. The hues we usually see in gems depend on having a full spectrum of white light present. If you’ve got but that entering the gem, what comes out could even be different. This is why some gems, like alexandrite, change color between natural and artificial light. Some gemstones also can change colors when viewed in several varieties of artificial light.

Critical Angle

critical angle in a lake If you’ve ever spent a day at a lake, you’ve probably noticed a refraction effect called the critical angle. During the day, sunlight passes into the lake. However, for an instant just before sunset, the light reflects off the water rather than passing into it. Looking within the direction of the sun becomes difficult due to the glare. Whether sunlight passes into the water or reflects off depends on the angle at which it hits the water. When the light reaches the critical angle, the surface reflects it. The critical angle effect occurs with gemstones, too, and affects gem faceting specifically. If you haven’t already experienced this, please do this little experiment. While facing the sun, inspect quartz. Turn it this way which to examine the maximum amount of the inside as you can. Most of the time, you’re looking all the way through the crystal. Once in a while, though, one among the sides will act as a mirror and reflect the sun towards your eyes. What happens when the light reaches the critical angle in your field of view.

brilliance fire and scintillation


Gem cutters must understand critical angles to bring out maximum brilliance in their cuts. A gem’s brilliance, in essence, is that the light that’s reflected off the bottom or pavilion facets back towards the viewer’s eye. From the above examples, you must understand that the connection of the light to the bottom facets is below the gem’s critical angle. In theory, the higher the RI, the greater the potential brilliance of the gemstone. However, really, brilliance involves numerous other factors that rarely have any practical value. For example, a gem not cut to ideal proportions or not polished well will have significantly less brilliance. Yet another factor is color saturation. The deeper the gem color, the more light is absorbed. Thus, the brilliance suffers. Try this experiment. Get yourself some well-cut and polished quartz and aquamarine gems. (Cut plays a big role in a gem’s brilliance). Quartz and aquamarine have very low RI’s. On the opposite hand, diamond has one among the highest. Carry your well-cut quartz or aquamarine around with you. you’ll find they need more brilliance than some of the diamonds you’ll see!


Gemstone scintillation, a multitude of tiny flashes of light, may be a property closely related to brilliance. The number and orientation of the facets determine the quantity of scintillation. The gem’s crown facets break up the light of the pavilion facets, causing the flashes. While gems with high scintillation usually have high brilliance, this isn’t always the case. Left, this gem displays high brilliance. it’s nice scintillation on the sides but little within the middle. Right, this gem has both high brilliance and high scintillation, with a lot of little sparkles throughout.


gemstone window Recall exploring through a quartz to seek out the critical angle? you’ll also see another optical phenomenon during that test. Windowing is once you can look straight through the crystal, without light reflecting off a side. Economics has more to try and do with gem cutting than aesthetics. That’s just a fact of life. Lapidaries cut most gems to achieve maximum size when finished, instead of maximum beauty. Now, that always requires cutting the pavilion facets at angles well off the critical angle. When this happens, you’ll see windowing within the finished gem. With the gem face up, you’ll see the deepest color and scintillation around the edges. However, you’ll look throughout the middle, the windowing area. Here, no light is reflected back, hence no sparkle, and the color is far lighter. If you’re unfamiliar with windowing, take the time to look for it. Once you see it, this effect becomes quite obvious. Small windows are common and have little effect on a gem’s beauty. Large windows, however, mar the looks of a gem significantly. Customers will take that into consideration when looking to form a sale.

Double Refraction and Birefringence

When light enters a gem, it’s refracted. If the light faces no restrictions aside from slowing down, gemologists call the gem isotropic. In isotropic materials, light passes every direction at the same speed and with the same color. This occurs in amorphous materials like glass, plastic, opal, and amber, also as minerals that form within the cubic system. These materials have one RI and one color. In the other five crystal systems, light becomes polarized. Thus, it vibrates in two or three planes. Each direction of light features a different speed and RI. This is called double refraction. Birefringence is the difference between the refractive indices of a gem. For example, if a stone features a high RI of 1.623 and another side RI of 1.617, the birefringence is 0.006. While some gems have three angles of refraction, measuring all three RIs during a faceted gem is difficult. So, simply measuring the range between the high and low RI suffices, rather than distinguishing all three. Thus, gemologists call all gems, aside from those within the cubic system or amorphous, doubly refractive. Each angle of refraction can have a different color. (Of course, colorless gems are the exception, since they don’t have multiple hues). Few gems show three colors, so this is often where the third refraction angle becomes important. (I’ll cover this in more detail under “Pleochroism”). Gemologists call stones with double refraction anisotropic. That means an unequal distribution of gemstone optical properties in a crystal. The term anisotropic also applies to physical properties, like minerals that vary in hardness.


In most doubly refractive gems, the difference between RIs is so small you can’t see it. You can still measure the difference with a refractometer. However, some gems have such an excellent difference between RIs it causes doubling or multiple images. For example, calcite features a birefringence of 0.172 and shows extreme doubling. calcite High birefringence is common in a few other gems, notably tourmaline and zircon. When looking into them, you’ll see a doubling of the back facets. This tells you immediately that you have a gem with high birefringence. Since this isn’t an optical property many gems possess, it’s an important clue for gem identification. However, not seeing strong doubling doesn’t mean a gem has low birefringence. If you’re looking straight down a gem’s C axis, you’ll see only single refraction. Sometimes, you’ll need to look around aside to check the doubling.

Crystal Habits and Refraction

A quick review of crystal habits will help explain why some crystals are singly, doubly, or triply refractive. Amorphous Amorphous materials haven’t any crystal structure or habit. they have one refractive index and one color. Isometric Because of the equality of the axes, minerals within the isometric or cubic system are singly refractive. Tetragonal Tetragonal minerals, and therefore the gems cut from them, will have double refraction. Light passing through the C axis are going to be refracted at a distinct speed than that on the shorter axes. If colored, tetragonal gems also will vary in hue. Obviously, colorless crystals won’t show two hues. Hexagonal In the hexagonal system, the light will refract at two speeds, one on the optic axis and another on the shorter, but equal length axes. If the gem is colored, the 2 directions will show at least slightly different hues. Orthorhombic In the orthorhombic system, although all the axes meet at 90° they all have different lengths. Hence, all three optic axes will refract the light at a different speed. Orthorhombic gems can potentially show three different colors. Monoclinic In the monoclinic system, all three axes are different lengths but only two meet at 90°. Thus, each optic axis will refract the light at a distinct speed. Each can potentially have a different hue. Triclinic In the triclinic system, none of the axes have an equivalent length nor meet at 90°. Again, each optic axis will refract the light at a different speed and each can display a different hue. Summary Only amorphous materials or minerals within the isometric system have one refractive index. they have a uniform color. Minerals within the tetragonal and therefore the hexagonal system has double refraction. They can also show two different colors. The other crystal systems, orthorhombic, monoclinic, and triclinic, have three unequal optic axes. Each will have a different angle of refraction and potentially three different colors.


dichroscope Pleochroism means showing multiple colors and results form birefringence. You’ll also encounter the term dichroism, which means two colors, or trichroism, which means three colors. Just as RI varies by the optic axis, so does the color in many occasions. Often, the colour difference is so slight you’ll need a dichroscope to examine it. For example, see the image to the right. With other gems, the difference is so extreme you’ll see both colors at the same time. Andalusite, with its green and orange pleochroism, is a superb example. You’ll also find extreme pleochroism in tourmaline and iolite. If properly cut, iolite displays blue to violet face, but pale yellow or colorless from the sides. (Be aware, iolite’s other properties come close to amethyst. The two are easily confused. However, a fast check out the gem from the side will distinguish it). Pleochroism Don’t confuse pleochroism with color zoning. Some stones, just like the ametrine pictured to the left, may have separate areas of color on an equivalent optic axis. This is entirely different from pleochroism.


Gemstone dispersion is that the spreading of white light into its component colors. once you see a rainbow coming out of a prism, you’re viewing dispersion. The fire of a diamond is another example. Although common to most gems, dispersion is rarely strong enough to be easily seen. Dispersion is easy to confuse with birefringence. With dispersion, each wavelength of light is refracted slightly differently. However, this has nothing to try to do with the gem’s optic axis. Diamonds, which crystallize within the cubic system and are singly refractive, have high dispersion. Dispersion is often a very important piece of information for gem identification. You’ll rarely see dispersion under 0.020, and that would be weak. So, if you see noticeable dispersion during a gem, you’d eliminate quartz (0.009), sapphire (0.018), and most other gems as candidates. The amount of fire, or dispersion, you see from a gem depends to an excellent extent on cut. The pavilion angles determine what proportion of light is reflected back to the top. On the crown, high angles emphasize dispersion, whereas low angles or a skinny crown will show considerably less. This explains why some diamonds appear to have far more fire than others. All diamonds have equivalent gemstone optical properties, including an equivalent dispersion. However, they don’t display it equally. When you become conversant in what proportion dispersion a well-cut diamond will display, you’ll use that to differentiate it from CZs. Diamonds have a dispersion of 0.044, very high within the world of gems. However, CZs have a way higher dispersion at 0.060. When you know what you’re trying to find, you’ll see it from a distance.


gemstone luster types gemstone luster types Gemstone luster is what proportion light is reflected off a smooth surface. This includes light from the pavilion facets as well as the surface. Diamonds have the very best luster of all gemstones: adamantine. In fact, adamantine literally means “diamond-like.” Gems like rubies and sapphires have sub-adamantine luster. Most transparent gems you’ll encounter will have vitreous or “glass-like” luster. Since photos don’t always capture luster well, you would like to examine some well-cut diamonds and colored stones to check the differences. Nevertheless, the image below will offer you some idea of the difference between a diamond with an adamantine luster (center) and vitreous colored stones (left and right). luster of gemstones Other sorts of luster include dull, metallic, pearly, silky, waxy, resinous, and greasy. Although the terms are somewhat subjective, they’re just about self-explanatory. Amber is typically resinous. Hematite is metallic. Charoite and coral are waxy. Also, gems can display more than one type of luster. for instance , some stones are often either sub-adamantine or vitreous. Chalcedony is typically vitreous but also can be greasy. Opal is typically vitreous but are often resinous. Some gems can display different lusters supported the orientation of its optical axis. Remember, consider the standard of lapidary work when assessing luster. Just because a stone shows a dull luster doesn’t necessarily mean that’s an actual property of the gem itself. It could just lack a decent polish. Conversely, stones like amber are often taken to a vitreous level of polish.

Optic Character

Although polarization splits light in two directions, not all the individual beams are polarized. Gems in the hexagonal and tetragonal systems only polarize light in one direction. The light passing down the optic axis remains unpolarized. This is the definition of a uniaxial gem. Sapphire, quartz, tourmaline, and zircon are common examples of uniaxial gems. Other doubly refractive gems have two optic axes, both of which are polarized. They are called biaxial gems. Since this occurs with all minerals in the orthorhombic, monoclinic, and triclinic systems, they’re more common. You can see a biaxial optic sign in the photo to the right. optic axis Gemologists also distinguish optic signs as positive, negative, or without signs.


The molecular structure of a crystal changes the energy that comes into it. We’ve seen that with selective absorption. This also happens with the invisible portion of the electromagnetic spectrum. In particular, if you place ultraviolet energy (UV) into a gem, some of it may change into visible light. this is often called fluorescence. gemstone fluorescence Some gems will continue to emit visible light after the UV is turned off. This is called phosphorescence. VIVID FLUORESCENT PHOSPHORESCENT QUARTZ & BARITE HALF GEODE When testing a gem for fluorescence, gemologists use two different frequencies, longwave (315 to 400 nm) and shortwave (200 to 280 nm). You’ll often get different results from the different frequencies, so test both ranges. During testing, note the hue (if any), intensity (weak, moderate, strong, or inert), and if the color is evenly distributed, zoned, or patchy. Fluorescence and Gem Identification If you’ve already tested a gem’s RI and optic sign, an ultraviolet test may help you narrow the possibilities. Don’t start your gem identification process with testing fluorescence, since most mineral species have specimens that are inert to ultraviolet. However, if one of your candidates shows green or orange, weak or strong, this is useful information. Ultraviolet testing is easy to conduct, though it poses some health risks, too. See “Ultraviolet Testing and Gemstone Identification” for more information. Fluorescence and Gem Grading Fluorescence can play a crucial role in gem grading. For example, diamonds fluoresce a variety of hues and at different strengths. Since sunlight contains plenty of UV, it’ll often affect their appearance. However, since 2008, the quality for diamond color grading is daylight-equivalent lighting with a UV component, so diamond color grades assigned since then should already account for the fluorescence factor. Burma rubies also are known for intense red fluorescence. This gem literally glows in the sunlight. In addition, oils used as fillers in emeralds and other gems often fluoresce. Checking for fluorescence may be a great way to detect this treatment since these fillers are nearly invisible in normal light.

Phenomenal Effects

Light does some wondrous things inside special gems. It can create stars and cat’s eyes, billowing clouds, and intense multicolored reflections. These special optical effects are why we cherish moonstones, pearls, opals, sunstones, alexandrites, labradorites, and other phenomenal gems.


Article Composed by : සම්පත් සමරසේකර Sampath Samarasekara Chairman: Gemological Institute of Ceylon Chairman: Youth Gem Professionals Association Chairman: Sampath Gems Director: Ceylon Sapphire Gems and Jewels Director: Ceylon Gem Fair International Chairman: Nanosoft Web Develop Company Direct WhatsApp:

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