Gemstone Glossary List
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This page contains the list of Gemstone Glossary from the book Gem Dealers' Secrets - Handbook for the Gem Buyer, written by Sondra Francis.
See Also: Gem Dealers' Secrets - Handbook for the Gem Buyer - Table of Contents
Gemstone Glossary List
- Abrade- to wear away; abrasion is caused by friction.
- Adamantine - diamond-like luster.
- Adularia - "flash" in moonstones created by microscopic inclusions.
- Amorphous - describes a substance with no precise patterning of atoms.
- Asterism - " star effect " in gems.
- Bi-color - describes a gemstone with two body colors visible, usually bi-color refers to tourmaline.
- Birefringence - difference in refractive indexes of the two axes in a doubly refractive mineral.
- Body color - the color of the main portion of the stone.
- Brilliance - the light that is reflected out of the gem; it is created from the light bouncing off internal facets.
- Carat - weight equivalent to one-fifth of a gram; used to weigh gemstones.
- Chatoyancy - "cat's-eye" effect in gem materials.
- Choker length - l4 to l5 inch length for necklaces.
- Clarity - refers to the internal "occupants" of the gemstone; any inclusions, flaws or general clearness of the gem.
- Cleavage - ability to separate along the plane of a crystal surface.
- Color change - ability of a gem to appear a different color under different light sources.
- Color zoning - uneven distribution of color within a gemstone.
- Crown - the portion of the gemstone above the girdle; the top part.
- Crown angle - the slope between the table and the gridle.
- Crystalline - describes substances with a precise atomic arrangement.
- Cultured - refers to pearls that have been made by the artificial implantation of a nucleus over which a nacre layer grows to form the pearl.
- Depth percentage - a ratio between the diameter of the stone and the total depth of the stone.
- Dichroism - The ability of doubly refactive materials to transmit different colors down different axes.
- Dispersion - the breaking up of white light into spectral colors.
- Doublet - an assembled gemstone with a crown portion of one material bonded to a pavilion portion of another material.
- Double refraction - the separation of light passing through a substance into two rays. This occurs in gems forming in all the crystals system except the cubic or isometric system.
- Dull - surface luster that does not efficiently reflect back light.
- Durability - overall toughness, resistance to breakage and scratches, and wearability of a gemstone.
- Fancy color - a color of a gemstone other than the most typical or well known color.
- Fancy shape - a gemstone shape that is other than round, oval, emerald cut or cushion shape.
- Fluorescence - ability to absorb ultraviolet light and emit visible light in return.
- Gold filled - describing a process of gold plating base metal for jewelry.
- Girdle - the circumference portion of the stone; the part that divides the crown from the pavilion.
- Grain - 1. a weight equivalent to one-quarter of a carat; used to weigh pearls. 2. also refers to cleavage directions in gems and crystals.
- Greasy - describes an oily luster.
- Hardness - scratchability; measured by Moh's scale.
- Ideal cut - a mathematically formulated set of proportions for a diamond that maximizes brilliance and dispersion.
- Inclusion - an internal crystal, void, impurity, fracture, or cleavage that is eye-visible or visible under l0X magnification.
- Karat - describes the fineness of gold; one unit is the equivalent of 1/24 part gold.
- Luster - quality of surface appearance which depends on its reflecting qualities.
- Matinee length - 20 to 24 inch length for a necklace.
- Melee - small round stones. Usually refers to diamonds, but can be any small round stones.
- Metallic - having a metal-like luster.
- Mohs Scale - scale from l to l0 that describes hardness.
- Momme - weight used for culture pearls; it is the equivalent of 3.75 grams.
- Nacre - layers of calcium carbonate that forms "pearly" part of a pearl.
- Opaque - describes substance that does not transmit light.
- Orient - describes the depth of luster in pearl; it is created by layers of nacre.
- Pavilion - the lower portion of the gemstone.
- Play of color - the flashes of color in an opal.
- Pearly - iridescent luster.
- Pleochroism - the ability of different axes in a crystal to transmit light at different rates; this is easily viewed by using a dicroscope.
- Reconstituted - man made gemstones created by using ground up gem materials forming an imitation of the original gem material.
- Refraction - bending of light within a substance.
- Refractive index - The measurement of the bending of light within a substance. It is abbreviated as R. I.
- Rough - gem material that has not been cut or fashioned.
- Rutile needles - a mineral that often forms as inclusions inside of other gem materials.
- Schiller - metal-like reflections from inclusions in feldspars.
- Scintillation - the reflection of light off of a facet surface, it is the "sparkle" of a gemstone.
- Semi-translucent - transmits a limited amount of light.
- Semi-transparent - transmits most light through a substance.
- Silky - quality of luster that is fibrous.
- Singly refractive - describes the manner in which light is transmitted through a cubic or isometric crystal substance; light is absorbed at the same rate at all angles.
- Specific gravity - ratio of the density of any substance to that of water at 4 degrees centigrade. It is abbreviated as S. G.
- Symmetry - refers to the balance of various elements in a gemstone, the evenness of facet shapes, parts, etc.
- Synthetic - a man-made gemstone that has the same chemical structure, optical and physical properties as a naturally occurring counterpart.
- Table - the top, and generally largest facet, on a gemstone.
- Toughness - overall durability of a gemstone including its resistance to breakage, chipping, and abrading as well as hardness.
- Translucent - transmits light but cannot be seen through.
- Transparent - all light passes through and it can be viewed through.
- Trichroism - the ability of some gems to absorb light at different rates through three axes; with a dichroscope three different colors can be observed when viewed from three different angles.
- Triplet - an assembled gemstone consisting of a top, middle, and bottom of different materials that have been bonded together.
- Vermeil - gold plated sterling silver.
- Vitreous - glass-like luster.
By Sondra Francis – Copyright © Sondra Francis, G.G. 1999
About the Author
Sondra Francis has scoured every major colored gemstone market in the world since 1978. She was a charter member of the American Gemstone Association and served as a board member. She was a founding member of the International Colored Gemstone Association. A true gem lover, Sondra has marketed her treasures on the wholesale and retail markets.
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Acknowledgments: A special thanks to Pam Dulgar, Alex Edwards, Cheryl Kremkow, Kate Kirby, Helen Mitchell, Carol Morgan Page, David Pond, Elaine Proffitt, and Ray Zajicek for their help.
Photographs: Bart Curren and ICA Gembureau ; Alex Edwards, Pearl Sales Institute ; David Dikinis
