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.