Gemstone Glossary

This is a glossary of technical terms commonly used in the gem and jewelry business.
 

Abrade - to wear away; abrasions are caused by friction.

Adamantine - diamond-like luster.

Adularescence - 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 characteristics in 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.

 

 
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