To identify gems, polariscopes employ polarized light. On top and bottom of the device, respectively, are two polarized filters. The vibrational planes of the polarizer and analyzer are distinct from one another. The field between them remains dark when the polarizer’s vibrational plane is perpendicular to the analyzer’s vibrational direction. The “crossed position” is the name given to this posture. Gems in this place can be examined to see if they are:
1. Isotropic 2. Anisotropic 3. Anomalously double refractive or an 4. Anisotropic aggregate
The polarizing plastic sheets (stretched polymers) used to make the polarizing filters for this instrument are constructed of polyvinyl alcohol that contains dichroic molecules. Older versions were made using tourmaline plates or the tiny orientated crystals of iodoquinine sulfate (herapathite).
Polariscope operation and potential observations
Turn on the light source, cross the polarizer and analyzer, and set the gemstone on the spinning platform slightly above the polarizer. You can choose from four possibilities by slowly rotating the stone while looking at the gemstone via the analyzer.
1. The stone appears dark throughout a 360° rotation. The stone is isotropic/single refractive.
2. Throughout a 360° rotation the stone blinks 4 times, light and dark. The stone is anisotropic/double refractive.
3. The stone will appear light all the time. The stone is a microcrystalline or cryptocrystalline aggregate (like, for instance, chalcedony).
4. The stone will show anomalous double refraction (ADR). It is isotropic/single refractive.
The first three behaviors shouldn’t present any issues for a novice user, but the fourth behavior (ADR) can be misunderstood and lead one to believe that the stone is double-refractive.
One way to avoid confusion when one detects ADR is to set the stone in its lightest position and then swiftly rotate the analyzer 90 degrees. When a gemstone exhibits ADR, it becomes substantially lighter and is single-refractive. The stone is double refractive if it stays essentially the same.
Course Content:Online/Offline Practical Gemology + Trading Program
Mine to End Customer Fast-track + Lifetime Service and Support 16 Days Online or Offline Sessions + Unlimited Revisions Unlimited Field Visits to Local Gem Fairs and Gem Mines ( Sri Lanka ) Lifetime Subscription to the support hotline Business Setup – Google and Physical Location Fully Customized Website + Online Store (CMS) + Training Social Media Integration and Guidance – Newsletters, Facebook, Instagram, LinkedIn, Twitter, WhatsApp,WeChat, Line, Tumblr YouTube Channel Setup and Guidance Gemstones Photography and Videography in Natural Background with Minimum Resources – Guidance Resources Introduction with Recommendation – Rough Gemstones, Cut and Polished Stones, Heat Treatment Persons, Gem Cutters, Laboratories, Jewelry Makers, Import and Exports
Course Content:Online/Offline Practical Gemology + Trading Program
Mine to End Customer Fast-track + Lifetime Service and Support 16 Days Online or Offline Sessions + Unlimited Revisions Unlimited Field Visits to Local Gem Fairs and Gem Mines ( Sri Lanka ) Lifetime Subscription to the support hotline Business Setup – Google and Physical Location Fully Customized Website + Online Store (CMS) + Training Social Media Integration and Guidance – Newsletters, Facebook, Instagram, LinkedIn, Twitter, WhatsApp, WeChat, Line, Tumblr YouTube Channel Setup and Guidance Gemstones Photography and Videography in Natural Background with Minimum Resources – Guidance Resources Introduction with Recommendation – Rough Gemstones, Cut and Polished Stones, Heat Treatment Persons, Gem Cutters, Laboratories, Jewelry Makers, Import and Exports
Emerald is the green to bluish-green variety of beryl, a mineral species that also includes aquamarine as well as beryls in other colors.
Gem experts differ on the degree of green that makes one stone an emerald and another stone a less-expensive green beryl. Some people in the trade tend to give the name emerald to any green beryl colored by chromium. But to most gemologists, gemological laboratories, and colored stone dealers, it is more correct to call a stone green beryl when its color is “too light” for it to be classified as emerald. Even among that group, however, there’s a difference of opinion about what’s considered “too light.”
FACTS
Mineral: Beryl
Chemistry: Be3Al2Si6O18
Color: Vibrant green
Refractive Index: 1.577 to 1.583
Birefringence: 0.005 to 0.009
Specific Gravity: 2.72
Mohs Hardness: 7.5 to 8
Emerald – Surface-reaching fractures in emerald are sometimes filled with essential oils, other oils, waxes, and “artificial resins” —epoxy prepolymers, other prepolymers (including UV-setting adhesives), and polymers to reduce the visibility of the fractures and improve the apparent clarity. These substances have varying degrees of stability in treated emeralds, and the volume of filler material present can range from insignificant to major amounts.
Clarity
In order to understand emerald inclusions, you must first understand their clarity. Emeralds are classified as a Type III gemstones. There are three types total Type I, Type II, and Type III gems. Type I gems typically form very clearly with no inclusions. Aquamarines, heliodor, and topaz are a few examples. Most gems qualify as Type II gems, usually showing some inclusions. Rubies, sapphires, and quartz are all examples of Type II gems. Type III gems almost always show inclusions, which is the category emeralds fall into. As a result, most emeralds are oiled for clarity.
The French have a term for these typical inclusions, called a “jardin” or “garden”. Inside the green gem, these inclusions resemble a garden, both being creations of mother nature. No two sets of jardins are the same, and they can even be used to identify individual gems.
Inclusions
Inclusions in emeralds are sometimes referred to as “jardin,” or “garden” because they can resemble moss or plant foliage. Emeralds with many inclusions should be treated with care since they are more vulnerable to damage due to the inclusions. Despite this, they are still far more durable than your finger.
Causes
A crystal inclusion (probably chromite) in an emerald.
Inclusions form because mother nature mixes whatever random elements are in the ground. Beautiful, transparent gems are the lottery prize of these formations. Of course, different locations will have different inclusions, though source-specific inclusions do not form in every emerald. Emerald inclusions vary with their location and may be used as a diagnostic tool for assessing the country of origin. Fractures and liquid inclusions are the most frequent, but inclusions in emeralds include can be any combination of the following:
Crystals
These are natural crystallization of other minerals inside the emerald. There are as many possible crystal inclusions as there are crystals. It is also possible to find a halo surrounding these inclusions, caused by a difference in melting temperatures of the crystal and the emerald during formation.
Liquid Inclusions
A three-phase emerald inclusion.
It is very common to have liquid inclusions filling cavities in emeralds. They can also form in those cavities with a gas bubble to make a two-phase inclusion. Especially common in emeralds is a three-phase inclusion where a gas, liquid, and crystal formation. In rare cases, the gas bubble or the included crystal may move within the cavity.
Fingerprints
Fingerprint inclusions in an emerald.
While more characteristic of rubies or sapphires, fingerprints are very possible in emeralds too. They can appear heavier and coarser but often overlap in appearances They often resemble the fingerprints we use to identify ourselves, though they can also look like wispy veils. Their appearance is a range, something applying to most inclusions.
Fingerprints can form with liquid and gas inside them, making them two-phase inclusions.
Needles – Needles are long thin crystals. Also falling in this category are hollow growth tubes leftover from crystal formation.
Fractures
Needle inclusions, and some out-of-focus fractures in an emerald
These fissures and cracks are by far the most common inclusion in emeralds. No one is entirely sure why they are so common in emeralds. One idea is that they are a natural byproduct of the crystal formation process, while another is that they are caused by harsh mining techniques.
The vast majority of emeralds are treated with oils and resins to enhance clarity issues caused by fractures. Between the oil and the fractures, they are to never be cleaned in an ultrasonic cleaner. This will remove the oil and will likely damage the emerald too. Re-oiling emeralds is not something that can be done at home, requiring specific oil and equipment.
Color Zoning
While not as common in emeralds as it is in other gems like sapphires or tourmalines, color zoning refers to different amounts of coloring in the emerald. For example, if one side is missing color and the other side is green. While this is an extreme example and very unlikely in emeralds, it is technically possible.
Phenomena
Cat’s Eye Emerald
Trapiche Emerald
Sometimes emeralds may have features that allow the display of a phenomenon called chatoyancy. More commonly called cat’s eye, this is caused by many fine needles or tubes being parallel to one another.
There has been an instance of an emerald that displays asterism, the star effect. However, this is not common in emeralds. It is also not to be confused with trapiche emeralds. Trapiche emeralds are a result of overall crystal formation, not specific inclusions like chatoyancy.
