Gemology is a very specific section of mineralogy. It basically studies minerals involved in the gem trade, either as precious or as decorative objects, making out certification of their authenticity. It aims to inform the industry and the general public about gem treatments, imitations and synthesis. From a commercial standpoint, a gem' s worth is enhanced according to its color, transparency, carat weight and the inclusions that tell us where it came from. Its analytical methods are strictly non-destructive, and standard gemological instruments such as the polariscope, refractometer, spectroscope and microscope, among others, are used for identification. If positive results cannot be reached, more sophisticated tests (EMPA, SIMS) relating to the physics and chemistry of minerals are then necessary.
Basic gemological tests start with an evaluation of the visual appearance of an object, its size and mounting, cut (proportions between the table and crown), color (if applicable), dispersion and purity (if colorless).
The polariscope distinguishes between isotropic and anisotropic material. The refractometer (based on Snell's law) reads the index of refraction, which is the most important of several properties.
The spectroscope shows absorption spectrum or dark lines.
The microscope will give clues to the surface and internal features of the material examined.
How to care for emerald
Emerald can be classified on the basis of its optical and physical properties, which vary in limited degree in regard to the mine of origin. Emerald is the only gemstone where inclusions and treatment are accepted by the trade. An emerald with few inclusions obviously is preferable, just as an emerald with intense color is more valuable than one whose color is faint. All emeralds are oiled to enhance color and minimize inclusions.
"Emerald" gave a name to a typical cut, but the stone can be faceted into any shape round, pear, rectangular, etc. To clean an emerald, warm water, mild soap and a soft brush work very well. Do not use an ultrasonic cleanser, as this will remove oil and show inclusions that were not evident before. Store emeralds separately from equal or harder gemstones to prevent scratching. Do not wear when exercising, and avoid rapid temperature changes.
Physical properties (may vary slightly according to source area)
Optical properties (may vary slightly according to source area)
Emeralds very often are clouded by inclusions actually referred as "jardin" (garden). These can be cubic crystals of pyrite (called "carbon," because they appear black in transmitted light), calcite, tremolite needles, actinolite, biotite flakes and/or two and three phase inclusions (cavities containing a liquid and gas or, in the case of three inclusions, one in a solid phase).No matter what the growth mode, inclusions trapped inside a gem provide an indelible fingerprint of the ambient in which it was formed. They can be gaseous, liquid or solid and correlate to the chemical-physical phenomena taking place during the metasomatic reaction in which the gemstone was formed. Solid inclusions can be considered the most useful, as they contain minute fragments of the rocks involved in the reaction. Studying such inclusions accordingly complements other types of analysis in pinpointing the deposit of origin. Nonetheless, the limited number of conditions out of which emeralds emerge is a complicating factor, as different deposits can have similar characteristics. This makes it difficult to identify with certainty the exact deposit of origin.