Gemstone Glossary

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 refractive 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 – resistance to scratching, measured by the Mohs 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.

Gemstone Glossary

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