Garnet is often thought of as red, but these gemstones come in almost any color and are popular for jewelry of all kinds. If you want to buy this January birthstone, that’s great news. In the gem world, the garnet family is one of the most interesting. It’s not a single species, but rather a group of different species and varieties that make it up.
A very wide range. See “Garnet Varieties” and “Identifying Characteristics” below and listings for specific garnet species and varieties.
A3B2Si3O12. A = Fe, Ca, Mn, Mg. B = Al, Fe, Ti, Cr. See “Identifying Characteristics” below.
From the Latin granatus for “grain.” Many garnet deposits are small grains of red crystals in or on their host rock.
Isometric. Trapezohedron and dodecahedron forms are common. Cube and octahedron forms are extremely rare.
Varies by species, 1.72-1.95. See Gem Listings for specific varieties.
Varies by species, 0.014-0.057. See Gem Listings for specific varieties.
Most varieties are inert. Grossulars can show a variety of fluorescence.
See Gem Listings for specific varieties.
Isotropic. Some garnets may show anomalous birefringence. See “Identifying Characteristics” below.
Vitreous, inclining to resinous in grossular, andradite, and some almandines.
3.40-4.30 (See Gem Listings for specific varieties).
Transparent to opaque
Will focus on the things that all garnets have in common and give a quick overview of how different they are. Garnets are not like minerals like beryl or corundum, which are all the same species but have different colors because of trace elements. They come from different species and are never found in their pure state. They are always mixed with other types of garnets, and they are never alone. They are called solid-state series or a blend because they are made up of different minerals. Some of these blends have unique features and are known as different types of garnets in their own right. What makes them all garnets is that they all have the same crystal structure and the same properties.
Almandines are the most common gemstone in the family of garnets. They come in a wide range of colors, and they are the most common in the family. The combination of almandine and pyrope is the dark red variety that people think of when they think of garnets.
There are very few andradites in the world, and they are one of the rarest. They have the most dispersion out of all garnets, with even more fire than diamonds. Demantoids, a type of andradite, are very valuable.
It is very rare for grossulars to be red or dark in color. However, they come in every color, even white, except blue. Their light to medium tones and bright colors make them great for making jewelry. Tsavorites have an emerald-like green color and can be sold for a lot of money. Hessonite “cinnamon stones,” on the other hand, are very popular and cheap.
It isn’t possible to see through hydrogrossulars, which are usually blueish green in color. They can also be pink, white, or gray in color. The classification of hydrogrossular as a garnet species is exciting.
There is a red color in chrome pyropes that can match rubies. There are some dark stones, though.
Spessartites, also known as spessartines, are a type of garnet that isn’t very common. They come in a lot of different shades of orange. Mandarin garnets, a type of spessartite with a bright orange color, are very popular.
Uvarovites are the rarest member of the garnet family. They have a dark, rich green that looks like an emerald, and they are very rare. Facetable material is even rarer and always small. Non-Gem Garnet Species Non-gem garnet species include goldmanite, henritermierite, kimzeyite, majorite, schorlomite, and yamatoite. These garnets might be of interest to people who collect rare mineral specimens. Blends Some people assume these blends are types of garnet, not sub-types of the above species.
Rhodolites are a mix of pyrope and almandine that have a purple color.
Malaya or Malaia Garnet
In the past, this term was used to describe garnets that didn’t fit into any other categories. Now, gemologists know that malaya or malaia garnets are a mix of pyrope and spessartite, and they call them that.
Color Change Garnet
Color shift garnets, which turn blue when exposed to artificial light, have been identified in recent decades. Blue garnets with purple flashes under incandescent light were discovered in Madagascar in the late 1990s. A pyrope-spessartite mixture makes up these color-changing stones. A dramatic color shift from red to purplish red can be seen in some Idaho garnets. These are a mixture of almandine and pyrope.
The following species are known to blend:
Andradite-grossular (also known as grandites or Mali garnets)
Garnet identification is difficult. Several new blends have been discovered in East Africa in the last fifty years. There’s no reason to suppose that all of the conceivable combinations have been found. We don’t know where gemologists will go in the future. Garnets have a lot in common at the molecular level, despite their differences. For those who aren’t interested in science, here’s a visualization that, while not scientifically sound, can assist illustrate the point. If your hand were a model of a garnet molecule, the arrangement of atoms represented by the palm would be shared by all garnets. The atoms represented by your fingers, on the other hand, are interchangeable. To put it another way, various atoms can live on your fingers while the palm stays the same. Any time the chemistry is altered, a new species emerges. Even if the structure and related features of a finger stay the same, changing the atoms produces a distinct species (or very nearly so).
Chemistry The chemistry of garnets, of course, varies significantly more than the hand model can fully reflect. The chemical composition of the gem garnet species is shown below.
As you can see, chemistry comes in a variety of forms. Despite this, they all have a similar core structure. In the isometric system, garnets crystallize. The trapezohedron and dodecahedron are the most popular shapes. Surprisingly, they are rarely found in the shapes of cubes or octahedrons, which are the most prevalent shapes of other isometric minerals. Garnets come in a variety of sizes and shapes, including enormous, granular, and tumbling pebbles. Rhodolite has been described as one part almandine and two parts pyrope by gemologists for decades. Garnets, on the other hand, are not so straightforward. Rhodolite stones, like all other garnets, contain some of the other species as well. Garnets are never as simple as having two elements, even if they are present in trace proportions. Furthermore, a solid-state series such as an almandine-pyrope blend does not imply that it is a mixture, Fe3Al2Si3O12 and Mg3Al2Si3O122. Instead, it denotes the presence of both Fe and Mg in the structure.
Are There Any Pure Garnets? Garnets do not originate as a single pure species in nature. Roughly 83% pyrope, 15% almandine, and about 2% different garnets were found in the purest gem-quality pyrope ever discovered. Almandine and grossular are in the same boat. You’ll find that 80% is about as pure as it gets. Andradite and spessartite garnets, on the other hand, have been discovered to be up to 95% pure. There have been discovered non-gem-sized, colorless garnets that are 97% pure pyrope. It’s something to inspire garnet (or purity) lovers.
The almandine-pyrope and pyrope-spessartite series of garnets were once thought to constitute a straight-line sequence. However, this is insufficient to explain the increasingly complex mixtures we see. A two-dimensional graph with almandine, pyrope, and spessartite marking the three corners is a more helpful description. The chemistry of a gem is almost never found on one of the flat sides. It’s actually a point inside the triangle that indicates how much of each ingredient is present. A three-dimensional model is optimal for total accuracy. Andradite, grossular, and uvarovite can all be added to the formula in this way. Grossular and andradite are found in practically all garnet blends, however they are less prevalent. This graph can be used to show how much of each of these species are present in a single specimen. Understanding garnet mixes is crucial for gemologists. The mixes of today’s garnets show a great deal of variation. Unless it’s a popular variant, garnets are usually named after their two principal species for identification purposes. Simply put, garnets are not simple two-species minerals. Gemologists used to classify garnets based on their chemical composition. This terminology is still in use. Pyralspites are garnets that have Al (aluminum) in the B position in their chemical formula (for pyrope, almandine, and spessartite). Ugrandites are garnets having Ca (calcium) in the A position (uvarovite, grossular, and andradite).
Optics Chemistry has a big role in these qualities. Isotropic minerals include pyrrope, almandine, and spessartite. Uvarovite, grossular, and andradite, on the other hand, are birefringent due to the big Ca (calcium) atom. This could be due to strain, but it’s more likely owing to structural issues. Under the microscope, grossular and andradite are almost invariably zonal, often twinned, and clearly not isotropic.
Color Due to garnet’s tremendous range of overlapping colors, gemologists can’t identify this gem on the basis of color alone. This information is for reference only.
Uvarovite: dark green.
Grossular: colorless, white, gray, yellow, yellowish green, green (various shades: pale apple green, medium apple green, emerald green, dark green), brown, pink, reddish, black.
Andradite: yellow-green, green, greenish brown, orangey yellow, brown, grayish black, black. The color is related to the content of Ti and Mn. If there’s little of either element, the color is light and may resemble grossular.
Pyrope: purplish red, pinkish red, orangey red, crimson, dark red. Note: Pure pyrope would be colorless; the red colors come from Fe + Cr.
Almandine: deep red, brownish red, brownish-black, violet red.
Malaia: various shades of orange, red-orange, peach, and pink.
Rhodolite: usually has a distinctive purplish color.
Synthetics The gem world has been influenced by synthetic garnets. Synthetic garnet was the dominant diamond simulant prior to the introduction of cubic zirconia (CZ) in the late 1970s. These synthetic stones are still available, albeit in a reduced quantity in today’s market. The first synthetic garnet available on the market was YAG, or yttrium aluminum garnet. YAG is colorless in its purest form. It may, however, be made in practically any hue. The vast variety of refractive indices and specific gravity is due to the dopants employed for coloring. Each property has a colorless YAG near the bottom. YAG is not brittle and lasts a long time. However, for a diamond equivalent, its dispersion is a little modest. Gadolinium gallium garnet, or GGG, has a wide dispersion (.038). Yttrium is substantially more expensive than gadolinium and gallium. GGG, on the other hand, is a fantastic alternative, with a dispersion similar to diamond (.044). The coloring dopants, like YAG, are responsible for the wide range of refractive index and specific gravity. Each attribute has a colorless GGG near the bottom. CZ, which is less expensive, has mostly supplanted GGG in jewelry today. These synthetics, however, are still available in a variety of colors. Many lapidaries choose them because they cut lovely jewels.
Enhancements Proteus was a shape-shifting sea god in Greek mythology. His name now has the meaning of someone who can alter their appearance or principles quickly. The only garnets that are frequently handled are those known as “Proteus garnets.” Proteus will be created from a few almandine-pyrope diamonds from the United States. All of the other personalities are resistant to change. A thin layer of metals is applied to the stone’s surface during this treatment. It takes on a twofold appearance as a result of this. Proteus garnets feature a dark gray, metallic sheen in reflected light, similar to hematite. The dark red shows through in transmitted light.
Stone Sizes Garnet crystals are typically tiny, ranging in size from microscopic to around 6 inches in grossular. Many deposits are made up of tiny crystal grains embedded in or on the host rock. Garnets in granite with poor outward shapes, such as the almandine from Gore Mountain, New York, which has a diameter of 60 cm, can be much larger. In Brazil, a few spessartites weighing several pounds have kept their clarity and exquisite color. These are, however, quite rare. A garnet crystal typically measures half an inch to an inch in diameter.
Garnets should be cleaned with warm water, soap, and a soft brush. Garnets, despite their hardness and toughness, are heat sensitive. Excessive heat should be avoided.
Article Composed by : සම්පත් සමරසේකර Sampath Samarasekara
There are six crystal systems. All minerals form crystals in one of these six systems. Although you may have seen more than six shapes of crystals, they’re all variations of one of these six habits. Each system is defined by a combination of three factors:
How many axes it has.
The lengths of the axes.
The angles at which the axes meet.
An axis is a direction between the sides. The shortest one is A. The longest is C. There is a B axis as well and sometimes a D axis.
The Isometric System
The first and simplest crystal system is the isometric or cubic system. It has three axes, all of which are the same length. The three axes in the isometric system all intersect at 90º to each other. Because of the equality of the axes, minerals in the cubic system are singly refractive or isotropic.
The isometric crystal system has three axes of the same length that intersect at 90º angles.
Minerals that form in the isometric system include all garnets, diamond, fluorite, gold, lapis lazuli, pyrite, silver, sodalite, sphalerite, and spinel.
Minerals that form in the isometric system form in one of these three basic shapes.
The Tetragonal System
The tetragonal system also has three axes that all meet at 90º. It differs from the isometric system in that the C axis is longer than the A and B axes, which are the same length.
The tetragonal crystal system also has three axes. Axis C is longer than axes A and B, which are the same length.
Minerals that form in the tetragonal system include apophyllite, idocrase, rutile, scapolite, wulfenite, and zircon.
Minerals that form in the tetragonal system form in one of these three basic shapes.
The Orthorhombic System
In this system, there are three axes, all of which meet at 90º to each other. However, all the axes are different lengths.
The orthorhombic system has three axes, each of which is a different length. These axes intersect at 90º angles.
Minerals that form in the orthorhombic system include andalusite, celestite, chrysoberyl (including alexandrite), cordierite, iolite, danburite, zoisite, tanzanite, thulite, enstatite, hemimorphite, fibrolite/sillimanite, hypersthene, olivine, peridot, sulfur, and topaz.
Minerals that form in the orthorhombic system form in one of these three basic shapes.
The Monoclinic System
The previously discussed crystal systems all have axes/sides that meet at 90º. In the monoclinic system, two of the axes, A and C, meet at 90º, but axis B does not. All axes in the monoclinic system are different lengths.
The axes in the monoclinic system are all of different lengths. The A and C axes intersect at 90º, but axis B does not.
Minerals that form in the monoclinic system include azurite, brazilianite, crocoite, datolite, diopside, jadeite, lazulite, malachite, orthoclase feldspars (including albite moonstone), staurolite, sphene, and spodumene (including hiddenite and kunzite).
Gems that form in the monoclinic system form in one of these three basic shapes.
The Triclinic System
In the triclinic system, all the axes are different lengths. None of them meet at 90º.
None of the axes in the triclinic system intersect at 90º and all are different lengths.
Minerals that form in the triclinic system include amblygonite, axinite, kyanite, microcline feldspar (including amazonite and aventurine), plagioclase feldspars (including labradorite), rhodonite, and turquoise.
Gems that form in the triclinic system form in one of these three basic shapes.
The Hexagonal System
The crystal systems previously discussed represent every variation of four-sided figures with three axes. In the hexagonal system, we have an additional axis, which gives the crystals six sides. Three of these are equal in length and meet at 60º to each other. The C or vertical axis is at 90º to the shorter axes.
The hexagonal system has four axes. Three are equal in length and intersect at 60º. The longer C or vertical axis intersects the other shorter axes at 90º.
Minerals that form in the hexagonal system include apatite, beryl (including aquamarine, emerald, heliodor, and morganite), taaffeite, and zincite.
Gems that form in the hexagonal system form in one of these two basic shapes.
The Trigonal Subsystem
Mineralogists sometimes divide the hexagonal system into two crystal systems, the hexagonal and the trigonal, based on their external appearance. (Corundum, both ruby, and sapphire, is sometimes described as trigonal). However, for gemological purposes, the above six categories are sufficient.
Most gem guides will list trigonal crystals as hexagonal. These crystals are sometimes distinguished from hexagonal crystals because of their appearance.
Gem Material Without Crystal Systems
Amorphous materials are not minerals. Thus, they don’t form in any of these crystal systems. Examples of amorphous materials used as gems include amber, glass (including obsidian), ivory, jet, moldavite, and opal.
Some materials used as gems may contain crystals of minerals but can’t themselves be described as crystals because they don’t have a uniform crystal structure. These materials are called polycrystalline.
Article Composed by :
Chairman: Gemological Institute of Ceylon
Chairman: Youth Gem Professionals Association
Chairman: Sampath Gems
Director: Ceylon Sapphire Gems and Jewels
Director: Ceylon Gem Fair International
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A gemstone’s optical properties can attract our eyes so it gives a cut and polished stone a unique character. However, the Physical Properties of Gemstones are also important. They determine a gem’s durability, guide gem cutters when they cut and set, and help us gemologists identify gemstones.
Specific Gravity – Physical Properties of Gemstones
Specific gravity (SG) or density refers to how much something weighs in relation to its size. For example, a cubic centimeter of steel is much heavier than a cubic centimeter of styrofoam. SG is expressed as the relationship to an equivalent volume of water. For example, a gem with a specific gravity of 3 weighs three times as much as the same amount of water. In gemology, the terms specific gravity and density are interchangeable.
Specific Gravity Values of Popular Gemstones
As you see from the chart, few gems share a similar SG range. This makes SG one of every of the foremost useful gemstone physical properties you can have for identification. However, measuring specific gravity is difficult and time-consuming. Thus, you normally only conduct this test when necessary. (See “The Art and Science of Identifying Gemstones” for brand spanking new identification procedures that don’t typically require SG testing). Using specific gravity to Estimate Gem Weight When you’re buying and selling gems, knowing the SG of a gem can assist you to make the proper choice. For example, a one-carat opal with an SG of two would be much larger than a one-carat sapphire with an equivalent shape. Why? Because sapphire has an SG of 4. Let’s say you would like to seek out a replacement stone for a jewelry setting. While settings are measured in millimeters, gems are often sold by weight. If you order a one-carat sapphire to exchange a 1-carat opal, you’re certain an enormous surprise! If you recognize your gems well, you’ll estimate their weight by sight based on their SG.
Hardness and Toughness – Physical Properties of Gemstones The gemstone’s physical properties of hardness and toughness are often misunderstood. Their scientific meanings differ from their everyday meanings.
Scientifically, hardness is defined strictly because of the ability to resist scratching. Gemologists use the Moh’s Scale to define gemstone hardness. the scale runs from 1 to 10, with a selected mineral representing each number or unit. Diamond is the hardest at 10. Ruby comes in at 9, and so on. Each mineral on the scale will scratch softer stones, those below it. In turn, harder stones, those above them, will scratch it. Minerals of an equivalent hardness won’t scratch one another. 10 Diamond 9 Corundum 8 Topaz 7 Quartz 6 Feldspar 5 Apatite 4 Fluorite 3 Calcite 2 Gypsum 1 Talc
Hardness has a very important effect on how well a gem will wear as jewelry. As a general rule (though exceptions abound), stones of hardness 7 or more will wear well. Since common dust consists largely of quartz (hardness 7), anything softer will eventually lose its polish. Even just wiping the dust off of a soft gem (below 7 in hardness) will cause fine scratches. Over time, these fine scratches accumulate and diminish the polish.
Toughness Hardness has nothing to try and do with durability or toughness. Toughness or tenacity is defined because the ability to resist being hit. as an example, compare glass and wood. Scientifically, glass is far harder than wood. it’ll easily scratch the wood. However, you can hit a wooden board quite hard with a hammer without breaking it, yet glass will shatter with the slightest impact. So, while harder, glass isn’t nearly as tough as wood. You may not find toughness listed among gemstone physical properties in standard reference books. it’s no standard measurement procedures or units beyond verbal descriptions.
Cleavage – Physical Properties of Gemstones
Gemstone cleavage is a weak bond between the molecules of a mineral in certain planes in its crystal structure. you can best understand cleavage as a property of gemstones by comparing a gem to wood. Wood can split easily along the grain. However, splitting it across the grain is difficult. Some gems even have a direction along which they will easily split. this is often the cleavage plane. While cleavage affects toughness, it’s not related to hardness. Diamond is the hardest material known. However, since it’s cleavage planes, you’ll split it with a chunk of steel. Diamonds can break during normal wear. Cleavage fractures always run parallel to at least one plane of the first crystal’s surface. They’re always straight, flat, and difficult to examine if they’re inside the gem. you’ll spot them by the rainbow of colors that comes off a flat plane when light hits it at the right angle. Although hard to ascertain when small, cleavage fractures are vital for identifying and valuing a gem. Additionally, they indicate a weakness that would expand and ruin the gem.
Gemologists describe cleavage in terms of how easily the material will part. the standard terms range from perfect, which separates very easily, to good, fair, and poor. you’ll come upon other terms, like imperfect. However, these are used less frequently. Another thing about descriptions is the number of cleavage planes. Some gems, like topaz, only have one direction of cleavage. Since topaz’s cleavage plane runs parallel to the bottom of the crystal, lapidaries usually cut it off at this axis. Thus, topaz is fairly durable despite its cleavage plane. Other stones, like feldspar, have cleavage on every crystal face. This makes cutting and setting problematic.
Please note that current cleavage terminology is a smaller amount than accurate. Take topaz, again. Because it’s described as having perfect cleavage, faceters realize it is often cut with minimum care. On the opposite hand, spodumene is an absolute monster to chop since it separates so easily. Still harder, diaspore comes during a class by itself. Yet, spodumene and diaspore are listed as having perfect cleavage, an equivalent to topaz and diamond. So, if you’re judging how well a stone will wear, look deeper into the cleavage than the easy listings.
Diamonds and topaz wear well. They’re commonly used as ring stones. However, kunzite, pink spodumene, and a few other gems would make very risky ring stones.
Fractures – Physical Properties of Gemstones
Gemologists also describe how a mineral breaks in ways aside from along cleavage directions. They call this fracture. (Cleavage fractures are always flat, which makes them easy to spot and distinguish from other fractures). Although not always easy to call, fractures may offer you clues for gem identification. you’ll nearly always find fractures on the girdle or culet of a gem with a high-powered microscope. Of course, you’ll have better luck finding them on rough material. Fracture types include conchoidal, fibrous, splintery, granular, uneven, and hackly. The names are supported by what the fractures resemble. the foremost common sort of fracture is named “conchoidal”. You’ll see these on everything from glass to ruby.
Thus, they won’t help much with gem identification. However, discovering one among the less common fracture types would be a crucial clue. Keep in mind that fracture has nothing to try and do with the gemstone’s physical properties of hardness or toughness. Corundum is one among the foremost durable gems and it shares conchoidal fractures with glass, one among the foremost brittle. You can easily spot most of those fractures.
Conchoidal Typically, this fracture seems like an impact of a shell. If the fracture is a smaller amount complete, you’ll still see concentric banded lines during a curved section.
Fibrous Tiger’s eye gems have fibrous fractures.
Splintery Jade, ivory, and petrified wood (fossilized wood) often have splintery fractures. Be careful to not confuse fibrous and splintery. The difference is one among scale. Fibers are thin and fine, while splinters are usually thicker and coarser.
Granular fractures are common to lapis lazuli and maw-sit-sit.
Uneven Uneven fractures are often seen in sodalite and coral.
Hackly You’ll find hackly (sharp and jagged) fractures more commonly in metallic minerals.
Parting Like cleavage, parting occurs on a flat plane parallel to at least one of the crystal surfaces. Unlike cleavage, this results from gemstone twinning, where the crystal grew in overlapping layers. These layers have distinct thicknesses. Whereas a mineral with cleavage will have it in every specimen, parting only appears occasionally. It’s not present in every sample of a mineral species. for instance, you’ll find parts in some star rubies but not all of them. Star sapphires and rubies commonly contain parting. It’s somewhat common in chrysoberyl and quartz. You’ll usually see undercutting on the parting planes, as within the example pictured below. Undercutting represents a significant weakness during a gem and can greatly decrease its value and wearability.
Stability – Physical Properties of Gemstones
Stability refers to a gem’s ability to stay the same. Although most gems are very stable, don’t take that without any consideration. variety of things or sensitivities can affect the stability of certain gems. you ought to consider sensitivities generally, and light sensitivity especially, before you acquire a new gem, especially one you haven’t worked on. Leaving your beautiful, valuable, new acquisitions on your desk or during a bright case could cause them to change color or dry out.
Heat Sensitivity The most common gem stability problem is heat sensitivity. Gems don’t mind getting hot. Rather, the speed of change affects them. Thermal shock usually occurs during the cutting or setting of a gem. Lapidaries and metalsmiths need special training on the way to handle different gems to avoid thermal shock.
Opals are so heat sensitive they even need special care when worn. you’ll cause them to crack by walking from a heated room into the winter cold or from an air-conditioned room into the complete summer sun. Since opals contain water, drying also can cause them to crack. To avoid cracking, store opals in an air-tight container or with a little piece of damp tissue. When wearing opals, keep them under your clothing if you’re going between environments with heat variations.
Chemical Sensitivity Certain chemicals can affect the look or composition of a gem with chemical sensitivity. This poses a serious problem for porous gems. for instance, turquoise and lapis lazuli can change color by absorbing oils from your skin. Therefore, don’t wear these gems while functioning on your car, painting, gardening, or doing anything where you can come in contact with chemicals. Certain acids can easily dissolve carbonates. These minerals include malachite, pearl, rhodochrosite, and marble. remember that a lot of common households and jewelry cleaners contain these acids.
Pearl is notoriously sensitive to chemicals. Always placed your pearl jewelry last when you’re getting dressed. Hairspray and atomized perfumes can ruin them.
The colors of some gems will fade if exposed to enough light. Such light-sensitive gems are called “evening stones,” since they’re best reserved for evening wear when they’re not exposed to sunlight. Even display case lights can damage light-sensitive gems. Thus, take care when displaying these gems for sale. (In addition, display lights can produce enough heat to dehydrate opals). Many gems suffer from light sensitivity to some degree. Some brown and gold topaz will fade slowly over time. As kunzite loses its color, it also loses a lot of value. Even within an equivalent species, sensitivity can vary. Blue spodumene, for instance, is somewhat light-sensitive. However, hiddenite (green spodumene) is so light-sensitive you ought to keep these rare specimens covered and only take them out for brief periods.
Artificially irradiated gems also can fade when exposed to light or heat.
Optical properties largely determine a gem’s color. Streak, however, is one of the gemstone’s physical properties. It shows the color of a mineral without selective absorption live. To conduct a streak test, you powder a small little bit of a stone by rubbing the specimen across an unglazed porcelain tile or streak plate. Some stones have a streak color that differs considerably from what it shows under the light. for instance, most transparent colored stones, including emeralds, will show a colorless or white streak. Streak testing can help identify some stones. Hematite, an opaque metallic gemstone, features a reddish-brown streak, whereas hematite, a standard hematite imitation, features a brownish-black steak. However, don’t conduct this destructive test on finished stones. Test material in inconspicuous spots as a final resort only.
Magnetism Magnetism is one of the foremost misunderstood gemstone physical properties. The terms magnetism and magnetic refer to things possessing a magnetic field. Gemologists don’t use these terms to explain things that are attracted to magnets. Rather, they describe things that are magnets themselves. For instance, magnets attract ferrous metals. Hematite, a form of iron ore, would be attracted to a magnet. However, hematite itself isn’t magnetic, while hematine is. it’ll acquire metal objects. Tests for identifying gemstone magnetism usually involve suspending the gem from a thread and holding it near a magnet. Although they work, you’ll put in a lot of labor for the small information you’ll receive. Keep this property in mind, but know there are other, much easier, and customary gem identification tests.
Electrical Properties Minerals have a range of electrical properties.
Electroconductivity As the name implies, this is often the ability of a material to conduct electricity. Minerals with metallic bonding, like gold, silver, and copper, commonly possess this ability. a couple of minerals with partial metallic bonding are electrical semiconductors. Most gem minerals are nonconductors of electricity. However, there’s a crucial exception. Blue diamonds colored by artificial irradiation act as electrical insulators. Gemologists can distinguish them from naturally colored and synthetic blue diamonds by using thermal inertia meters.
Piezoelectricity Some minerals, like colemanite, quartz, and tourmaline, generate electricity when placed under pressure. This property, piezoelectricity, is common in several minerals to varying degrees. When pressure is exerted at the ends, electricity will flow and make opposite positive and negative poles. due to this property, quartz and tourmaline have various industrial applications. for instance, thin slices of quartz can control frequencies for radios and watches. Some pressure gauges use tourmaline. Tourmaline was used to measure the blast pressure of the first atom bomb in 1945.
Pyroelectricity Some minerals generate an electrical current when heated. Examples include boracite, colemanite (also piezoelectric), rhodizite, and sphalerite.
Frictional Electricity When rubbed, many gems commonly develop an electrostatic charge or frictional electricity. Notable examples include tourmaline and amber. If you rub them against something like wool, these gems gain enough charge to pick up ashes or small pieces of paper. the traditional Greeks recognized this quality in amber over 2,500 years ago. The word “electricity” comes from the Greek name for amber, Elektron.
Thermal Conductivity Some stones, notably crystalline gems, make excellent heat conductors. Because of their thermal conductivity, they’re going to draw heat far away from your fingers. Thus, they feel cool to the touch. Poor thermal conductors, like amber, glass, and plastic, feel warm to the touch. They don’t conduct heat far away from the body. If you concentrate on how a stone feels in your hand, you’ll often spot an imitation. When unsure, use a sensitive part of the body like your tongue or lips (but as long as you’ve recently cleaned the stone). Crystalline gemstone surfaces also will de-mist more rapidly than amorphous glass. Gemologists use thermal conductivity instruments to differentiate diamond, which conducts heat all right, from its simulants and imitations. Avoid drafts when testing, as they can change the readings. Thermal inertia meters measure how quickly the surface temperature of a gem changes when heated. This test also can help identify diamonds, since they need much higher thermal inertia than other gems.
Hot Point Testing Thermal reaction testing, or hot point testing, also can distinguish real gems from imitations. You’ll use a pin heated over a flame to get smoke and odors from gem samples and show reactions to high heat, like melting or bubbling. Since melting is common to plastic, amber, wax, and resins, that result means your sample either is one among those materials or was surface treated with them. Odors can often be diagnostic. Tortoiseshell and a few corals emit a burning hair smell, while jet, fossilized coal, features a petroleum aroma. Amber produces a resinous smell and whitish smoke. Plastic imitations have an acrid, chemical odor. Odors also can reveal wax and plastic surface treatments applied to gems. For instance, turquoise should haven’t any smell. However, you’ll detect the odor of any treatment on the surface of the gem. Hot point testing is another destructive test. Test material in inconspicuous spots as the last resort only.
Physical Properties of Gemstones Article Composed by : සම්පත් සමරසේකර
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