Gemstone Glossary List

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By Sondra FrancisMore from this author

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.
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

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Sondra Francis

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