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GIA Colored Gemstones - Key Terms
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GIA Colored Gemstones - Key Terms
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GIA Colored Gemstones - Key TermsAbrasions - ANS-Tiny nicks and pits caused by wear and damage to a gem's facet
edges or culet. (Colored Stones: Assignment 10)
Absorption spectrum - ANS-A pattern of dark vertical lines or bands shown by certain
gems when viewed through a spectroscope. (Colored Stones: Assignment 4)
Adularescence - ANS-The cloudy bluish white light in a moonstone, caused by
scattering of light. (Colored Stones: Assignment 4)
Agate - ANS-Chalcedony with curved or angular bands or layers that differ in color and
transparency. (Colored Stones: Assignment 20)
Aggregate - ANS-A mass of tiny, randomly oriented crystals. (Colored Stones:
Assignment 3)
Akoya - ANS-Common name for the Pinctada fucata oyster and the natural or cultured
pearls it produces. (Colored Stones: Assignment 16)
Allochromatic - ANS-A gem colored by trace elements in its crystal structure. (Colored
Stones: Assignment 4)
Alluvial deposit - ANS-A deposit where gems are eroded from their source rock, then
transported away from the source and further concentrated. (Colored Stones:
Assignment 2)
Amorphous - ANS-Lacking a regular crystal structure. (Colored Stones: Assignment 1)
Aragonite - ANS-A crystallized form of calcium carbonate found in nacre. (Colored
Stones: Assignment 16)
Assembled stone - ANS-Two or more separate pieces of material joined to form a unit.
(Colored Stones: Assignment 5)
Asterism - ANS-Crossing of chatoyant bands, creating a star in the dome of a
cabochon. (Colored Stones: Assignment 4)
Atom - ANS-The basic structural unit of all matter. (Colored Stones: Assignment 1)
,Aventurescence - ANS-A glittery effect caused by light reflecting from small, flat
inclusions within a gemstone. (Colored Stones: Assignment 4)
Background color - ANS-An opal's bodycolor, independent of its play-of-color. (Colored
Stones: Assignment 19)
Bead nucleus - ANS-A bead used as the core of a cultured pearl, usually made from a
freshwater mussel shell. (Colored Stones: Assignment 16)
Bleaching - ANS-A treatment that uses chemicals to lighten or remove color. (Colored
Stones: Assignment 6)
Blemish - ANS-Characteristic or irregularity confined to the surface of a polished
gemstone. (Colored Stones: Assignment 10)
Blue sheen - ANS-Trade term for a highly prized, vivid blue adularescence displayed by
the finest moonstone. (Colored Stones: Assignment 26)
Bodycolor - ANS-A gemstone's basic color, determined by its selective absorption of
light. (Colored Stones: Assignment 8)
Botryoidal - ANS-A crystal growth habit with a bumpy appearance similar to a bunch of
grapes. (Colored Stones: Assignment 20)
Boulder opal - ANS-Thin layers of precious opal, cut to include matrix. (Colored Stones:
Assignment 19)
Boule - ANS-A cylindrical synthetic crystal produced by the flame-fusion process.
(Colored Stones: Assignment 5)
Brilliance - ANS-Light that eventually returns to the eye after entering a gem through the
crown, reflecting off its pavilion facets, and exiting back through the crown. (Colored
Stones: Assignment 9)
Brilliant cut - ANS-Cutting style with triangular or kite-shaped facets that radiate from the
center toward the girdle. (Colored Stones: Assignment 9)
Cabochon - ANS-A smoothly rounded polished gem with a domed top and a flat or
curved base. (Colored Stones: Assignment 9)
, Calcareous concretion - ANS-A non-nacreous natural "pearl." (Colored Stones:
Assignment 16)
Calibrated sizes - ANS-Gemstone sizes cut to fit standard mountings. (Colored Stones:
Assignment 7)
Cameo - ANS-A gem carving style in which the design, often a woman's profile, projects
slightly from a flat or curved surface. (Colored Stones: Assignment 9)
Cavity - ANS-An opening that extends into a gem from the surface. (Colored Stones:
Assignment 10)
Centipedes - ANS-Tiny tension cracks in moonstone that interfere with adularescence
and reduce value. (Colored Stones: Assignment 26)
Ceramic process - ANS-A process in which finely ground powder is heated, sometimes
under pressure, to produce a fine-grained solid material. (Colored Stones: Assignment
5)
Certificate of origin - ANS-A document that indicates a stone's geographic origin, based
on its inclusions and trace element chemistry. (Colored Stones: Assignment 7)
Chalcedony - ANS-A cryptocrystalline quartz aggregate. (Colored Stones: Assignment
20)
Charge transfer - ANS-A process where the electrons that selectively absorb light are
passed back and forth between neighboring impurity ions. (Colored Stones: Assignment
4)
Chatoyancy - ANS-Bands of light in certain gems, caused by reflection of light from
many parallel, needle-like inclusions or hollow tubes. (Colored Stones: Assignment 4)
Chemical composition - ANS-Kinds and relative quantities of atoms that make up a
material. (Colored Stones: Assignment 1)
Chemical element - ANS-A substance that consists of atoms of only one kind. (Colored
Stones: Assignment 1)
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