Gemstone Glossary List

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
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