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GIA Colored Stones OG Test - Latest
Update With Complete Solution
Mineral - ANSWER A natural, inorganic substance with a characteristic chemical composition and usually characteristic structure.
Mixed cut - ANSWER A cutting style that combines brilliant-cut and step cut facets.
Abrasions - ANSWER Tiny nicks and pits caused by wear and damage to a gem's facet edges or culet.
Absorption spectrum - ANSWER A pattern of dark vertical lines or bands shown by certain gems when viewed through a spectroscope.
Adularescence - ANSWER The cloudy bluish white light in a moonstone, caused by scattering of light.
Agate - ANSWER Chalcedony with a curved or angular bands or layers that differ in color and transparency.
Aggregate - ANSWER A mass of tiny, randomly oriented crystals.
Akoya - ANSWER Common name for the Pinctada fucata oyster and the natural or cultured pearls it produces.
Allochromatic - ANSWER A gem colored by trace elements in its crystal structure.
Alluvial deposit - ANSWER A deposit where gems are eroded from their source rock, then transported away from their source and further concentrated.
Amorphous - ANSWER Lacking a regular crystal structure.
Aragonite - ANSWER A crystalized form of calcium carbonate found in nacre.
Assembled stone - ANSWER Two or more separate pieces of material joined to form a unit.
Asterism - ANSWER Crossing of chatoyant bands, creating a star in the dome of cabochon.
Atom - ANSWER The basic structural unit of all matter.
Aventurescence - ANSWER A glittery effect caused by light reflecting from small, flat inclusions within a gemstone.
Background color - ANSWER An opal's bodycolor, independent of its play-of-color.
Bead nucleus - ANSWER A bead used as the core of a cultured pearl, usually made from a freshwater mussel shell.
Bleaching - ANSWER A treatment that uses chemicals to lighten or remove color.
Blemish - ANSWER Characteristic or irregularity confined to the surface of a polished gemstone.
Blue Sheen - ANSWER Trade term for a highly prized, vivid blue adularescence displayed by the finest moonstone.
Bodycolor - ANSWER A gemstone's basic color, determined by its selective absorption of light.
Botryoidal - ANSWER A crystal growth habit with a bumpy appearance similar to a bunch of grapes.
Charge transfer - ANSWER A process where the electrons that selectively absorb light are passed back and forth between neighboring impurity ions.
Chatoyancy - ANSWER Bands of light in certain gems, caused by reflection of light from many parallel, needle-like inclusions or hollow tubes.
Chemical composition - ANSWER Kinds and relative quantities of atoms that make up a material.
Chemical element - ANSWER A substance that consists of atoms of only one kind.
Chip - ANSWER A damaged area on a gem, usually near the girdle.
Chrome tourmaline - ANSWER Trade term for a vibrant green tourmaline that's colored by traces of vanadium, chromium, or both.
Circled pearl - ANSWER A pearl with one or more grooved or ridged rings all the way around it.
Cleavage - ANSWER A smooth, flat break in a gemstone parallel to planes of atomic weakness, caused by weak or fewer bonds between atoms or both.
Cloud - ANSWER Any hazy or milky area that cannot be described as a feather, fingerprint, or group of included crystals or needles.
Cobbing - ANSWER Removing heavily included sections from a gemstone rough by carefully tapping it with a small hammer.
Color center - ANSWER A small defect in the atomic structure of a material that absorb light and give rise to a color.
Color Change - ANSWER A distinct change in gem color under different types of lighting.
Color range - ANSWER The selection of colors in which a gemstone occurs.
Color zoning - ANSWER Areas of different color in a gem, caused by variations in growth conditions.
Colorless impregnation - ANSWER Filling of pores or other openings with melted wax, resin, polymer, or plastic to improve appearance and stability.
Commercial market - ANSWER Market sector where average-quality gemstones are used in mass-market jewelry.
Conchiolin - ANSWER The organic "glue" in nacre that holds aragonite platelets together.
Conchoidal fracture - ANSWER A curved and ridged fracture in a gemstone, extending from the surface inward.
Consignment - ANSWER A selection of goods loaned to a dealer by another wholesaler or gem cutter.
Contact metamorphism - ANSWER Localized changes caused by an igneous intrusion that takes place where the magma meets the surrounding rock. New minerals may form due to temperature changes or introduction of fluids from the magma.
Core - ANSWER The earth's innermost layer.
Crazing - ANSWER The network of tiny fractures that develop when opal loses moisture.
Crown - ANSWER Top part of the gem above the girdle.
Crown-height to pavilion-depth ratio - ANSWER The relationship of the height of a gem's crown to the depth of its pavilion, judged by viewing its
Diffraction - ANSWER A special kind of interference phenomenon that breaks up white light into spectral hues.
Disclosure - ANSWER Clearly and accurately informing customer about the nature of the goods they buy.
Dopstick - ANSWER Wooden or metal stick that holds the preform during faceting.
Double refraction - ANSWER When a gem's crystal structure splits light into two rays that each travel at a slightly different speed and direction.
Doublet - ANSWER Two separate pieces of material fused oe cemented together to form a single assembled stone.
Durability - ANSWER A gemstone's ability to withstand wear, heat, and chemicals.
Dyeing - ANSWER A treatment that adds color or affects color by deepening it, making it more even, or changing it.
Eluvial deposit - ANSWER A deposit where gems are eroded from the source rock but remain in place close to the source.
Erosion - ANSWER The wearing away and transport of rock materials by natural forces.
Essence d' orient - ANSWER A mixture of clear varnish and fish scales used in making imitation pearls.
Extinction - ANSWER Dark areas in a faceted transparent colored stone.
Eye clean - ANSWER Description for a gem with no inclusions visible to the unaided eye.
Facet grade - ANSWER Gemstone rough that's transparent enough and of high enough quality to produce faceted gems.
Faceting head - ANSWER Device that holds the dopstick at precise angles to allow correct orientation during faceting and polishing.
Fantasy cut - ANSWER A free-form cut that can feature alternating curved and flat surfaces.
Feather - ANSWER A general term for a break in a stone.
Fingerprint - ANSWER Inclusions that forms a pattern that often resembles a human fingerprint.
Flame fusion - ANSWER A process in which powdered chemicals are dropped through a high-temperature flame onto a rotating pedestal to produce a synthetic crystal.
Floating zone - ANSWER A melt process where a heating unit passes over a rotating solid rod of chemicals until it forms a synthetic crystal.
Fluorescence - ANSWER Emission of visible light by a material when it's stimulated by ultraviolet radiation.
Flux growth - ANSWER A process in which nutrients dissolve in heated chemicals, then cool to form synthetic crystals.
Fracture - ANSWER Any break in a gem other than cleavage or parting.
Fracture (fissure) filling - ANSWER Using a filler to conceal fractures and improve the apparent clarity of a gem.
Goldstone - ANSWER An imitation of aventurine feldspar made of glass that contains small copper crystals.
Gonad - ANSWER The reproductive organ that produces eggs in females and sperm in males.
Grade - ANSWER A specific rough gemstone quality range, usually determined by color, size, clarity, and price.
Graduated strand - ANSWER A necklace with the largest pearl in the center and progressively smaller pearls approaching the clasp.
Grinding - ANSWER Giving approximate shape to a gemstone, or producing flat planes for polishing facets.
Group - ANSWER A family of gems from several closely related mineral species.
Habit - ANSWER The characteristic external crystal shape or form of a mineral.
Half-drilled - ANSWER Cultured pearl with a hole drilled halfway through to
permit mounting on a post.
Hank - ANSWER A number of cultured pearl strands bundled together.
Hardener - ANSWER A chemical that treaters mix with some resin to cause them to solidify.
Hardness - ANSWER How well a gemstone resists scratches. Usually expressed in terms of Mohs scale, with diamond the hardest and talc the softest.
Hatchery-bred - ANSWER Describes mollusks bred in laboratory tanks and grown in protected areas rather collected as adults in the wild.
Heat treatment - ANSWER Exposing a gem to rising temperature for the purpose of changing appearance.
Heavy minerals - ANSWER Minerals dense enough to become concentrated and separated for lighter ones by the action of surface water.
High grading - ANSWER In mining terms, theft of a mine's production by its workers.
Igneous rock - ANSWER Rock formed by the crystallization of molten material.
Imitation gem - ANSWER Any material that looks like a natural gem and is used in its place.
Imperial - ANSWER Trade name for the finest-quality, semitransparent jadeite with even, vivid green coloration.
Imperial Topaz - ANSWER A widely used trade term for gem-quality topaz of medium reddish orange to orange-red color.
Included crystal - ANSWER A mineral crystal trapped within a gem as it grows.
Indicolite - ANSWER Trade term for blue tourmaline.
Inorganic - ANSWER Composed of, or arising from, non-living matter.
Intaglio - ANSWER A design engraved into the surface of a gemstone.
Intended color zoning - ANSWER Visible face-up color zoning that was planned during the cutting process.
Interference - ANSWER Interaction of two light rays traveling in the same path.
Intervalence charge transfer - ANSWER A process where two impurity atoms separated by another atom can still exchange electrons to selectively absorb light.
Intrusion - ANSWER Large mass of igneous rock that crystallizes underground without reaching the surface.
Iridescence - ANSWER A rainbow effect created when light is broken up into spectral hues by thin layers.
Irradiation - ANSWER Exposing a gem to radiation to change or improve its color.
Isomorphous replacement - ANSWER Substitution of one chemical element for another in the crystal structure of a mineral.
body, and contains the cells that form pearl sacs and secrete nacre.
Mantle convection - ANSWER Circulation in the mantle that drives the movement of the earth's plates.
Mantle-tissue piece - ANSWER A small square of mantle tissue cut from a donor mollusk and implanted in a host mollusk with or without a bead.
Matching tray - ANSWER A grooved, neutrally colored, non-reflective tray, used to match sets of stones.
Melt process - ANSWER A synthetic-crystal growth method in which the chemical mixture is melted, then recrystallized.
Memo - ANSWER Buying agreement where a dealer entrusts merchandise to a client for inspection and approval without requiring immediate payment.
Metamict - ANSWER A mineral that's been broken down from a crystalline to a party amorphous state by emanations from radioactive impurities.
Metamorphic rock - ANSWER Rock altered by heat and pressure, or by heated fluids from magma.
Metric carat - ANSWER The international unit of measurement for gem weight. ( 1 carat equals 0.20 gram )
Microcrystalline - ANSWER An aggregate made up of individual crystals visible under magnification.
Middle market - ANSWER Market sector where better-quality gemstones are used in well-finished, moderately priced jewelry pieces.
Milk and honey - ANSWER a two-toned effect seen when a chatoyant gem is positioned at right angles to a light source.
Mine lot (mine run) - ANSWER A mixture of gem qualities that represents unsorted production from a particular mine.
Mineral - ANSWER A natural, inorganic substance with a characteristic chemical composition and usually characteristic structure.
Mixed cut - ANSWER A cutting style that contains brilliant-cut and step-cut facets.
New mine - ANSWER The colored texture category of jadeite.
Old mine - ANSWER The finest texture category of jadeite.
Optic axis - ANSWER Direction of single refraction in a doubly refractive gem.
Organic - ANSWER Produced by, or derived from, a living organism.
Orient - ANSWER Iridescence seen in some natural cultured pearls and mother-of-pearl.
Origin - ANSWER The geographical place where a gem was mined.
Oxidizing environment - ANSWER An oxygen-rich environment that surrounds a gem during heat treatment, causing it to absorb oxygen.
Paraiba tourmaline - ANSWER Trade term for rare, expensive, vibrant green to blue or violet elbaite tourmaline, originally found only in Brazil's Paraiba state.
Parcel - ANSWER A quantity of stones, sometimes of similar size and quality, perhaps from a single mine, but often from various sources, that's offered for sale together.
Parti-colored - ANSWER Gems that show color zoning with two or more colors.
Parting - ANSWER A flat break in a gemstone caused by concentrated included minerals parallel to a twinning plane.
Pavilion - ANSWER Lower part of a faceted gem below the girdle.
Pearl - ANSWER A nacreous, organic gem formed in the body of a mollusk.
Pearl sac - ANSWER Tissue that encloses an implanted bead nucleus and mantle-tissue piece, or the piece alone, and secretes nacre to form a cultured pearl.
Pegmatite - ANSWER An igneous rock formed from from cooling, once molten granite that follows fractures in its surrounding rock. It may contain very large crystals, and its shape is often thin and contorted.
