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GEM 220 Glossary
GIA Gemology 220 - Glossary Terms
| Term | Definition |
|---|---|
| Abrasions | Tiny nicks and pits caused by wear and damage to a gem's facet edges or culet. (Colored Stones: Assignment 10) |
| Absorption spectrum | A pattern of dark vertical lines or bands shown by certain gems when viewed through a spectroscope. (Colored Stones: Assignment 4) |
| Adularescence | The cloudy bluish white light in a moonstone, caused by scattering of light. (Colored Stones: Assignment 4) |
| Agate | Chalcedony with curved or angular bands or layers that differ in color and transparency. (Colored Stones: Assignment 20) |
| Aggregate | A mass of tiny, randomly oriented crystals. (Colored Stones: Assignment 3) |
| Akoya | Common name for the Pinctada fucata oyster and the natural or cultured pearls it produces. (Colored Stones: Assignment 16) |
| Allochromatic | A gem colored by trace elements in its crystal structure. (Colored Stones: Assignment 4) |
| Alluvial deposit | A deposit where gems are eroded from their source rock, then transported away from the source and further concentrated. (Colored Stones: Assignment 2) |
| Amorphous | Lacking a regular crystal structure. (Colored Stones: Assignment 1) |
| Aragonite | A crystallized form of calcium carbonate found in nacre. (Colored Stones: Assignment 16) |
| Assembled stone | Two or more separate pieces of material joined to form a unit. (Colored Stones: Assignment 5) |
| Asterism | Crossing of chatoyant bands, creating a star in the dome of a cabochon. (Colored Stones: Assignment 4) |
| Atom | The basic structural unit of all matter. (Colored Stones: Assignment 1) |
| Aventurescence | A glittery effect caused by light reflecting from small, flat inclusions within a gemstone. (Colored Stones: Assignment 4) |
| Background color | An opal's bodycolor, independent of its play-of-color. (Colored Stones: Assignment 19) |
| Bead nucleus | A bead used as the core of a cultured pearl, usually made from a freshwater mussel shell. (Colored Stones: Assignment 16) |
| Bleaching | A treatment that uses chemicals to lighten or remove color. (Colored Stones: Assignment 6) |
| Blemish | Characteristic or irregularity confined to the surface of a polished gemstone. (Colored Stones: Assignment 10) |
| Blue sheen | Trade term for a highly prized, vivid blue adularescence displayed by the finest moonstone. (Colored Stones: Assignment 26) |
| Bodycolor | A gemstone's basic color, determined by its selective absorption of light. (Colored Stones: Assignment 8) |
| Botryoidal | A crystal growth habit with a bumpy appearance similar to a bunch of grapes. (Colored Stones: Assignment 20) |
| Boulder opal | Thin layers of precious opal, cut to include matrix. (Colored Stones: Assignment 19) |
| Boule | A cylindrical synthetic crystal produced by the flame-fusion process. (Colored Stones: Assignment 5) |
| Brilliance | 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 | Cutting style with triangular or kite-shaped facets that radiate from the center toward the girdle. (Colored Stones: Assignment 9) |
| Cabochon | A smoothly rounded polished gem with a domed top and a flat or curved base. (Colored Stones: Assignment 9) |
| Calcareous concretion | A non-nacreous natural "pearl." (Colored Stones: Assignment 16) |
| Calibrated sizes | Gemstone sizes cut to fit standard mountings. (Colored Stones: Assignment 7) |
| Cameo | 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 | An opening that extends into a gem from the surface. (Colored Stones: Assignment 10) |
| Centipedes | Tiny tension cracks in moonstone that interfere with adularescence and reduce value. (Colored Stones: Assignment 26) |
| Ceramic process | 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 | A document that indicates a stone's geographic origin, based on its inclusions and trace element chemistry. (Colored Stones: Assignment 7) |
| Chalcedony | A cryptocrystalline quartz aggregate. (Colored Stones: Assignment 20) |
| Charge transfer | A process where the electrons that selectively absorb light are passed back and forth between neighboring impurity ions. (Colored Stones: Assignment 4) |
| Chatoyancy | 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 | Kinds and relative quantities of atoms that make up a material. (Colored Stones: Assignment 1) |
| Chip | A damaged area on a gem, usually near the girdle. (Colored Stones: Assignment 10) |
| Chrome tourmaline | Trade term for a vibrant green tourmaline that's colored by traces of vanadium, chromium, or both. (Colored Stones: Assignment 23) |
| Circled pearl | A pearl with one or more grooved or ridged rings all the way around it. (Colored Stones: Assignment 17) |
| Cleavage | A smooth, flat break in a gemstone parallel to planes of atomic weakness, caused by weak or fewer bonds between atoms, or both. (Colored Stones: Assignment 3) |
| Cloud | Any hazy or milky area that cannot be described as a feather, fingerprint, or group of included crystals or needles. (Colored Stones: Assignment 10) |
| Cobbing | Removing heavily included sections from gemstone rough by carefully tapping it with a small hammer. (Colored Stones: Assignment 9) |
| Color center | A small defect in the atomic structure of a material that can absorb light and give rise to a color. (Colored Stones: Assignment 4) |
| Color change | A distinct change in gem color under different types of lighting. (Colored Stones: Assignment 4) |
| Color range | The selection of colors in which a gemstone occurs. (Colored Stones: Assignment 8) |
| Color zoning | Areas of different color in a gem, caused by variations in growth conditions. (Colored Stones: Assignment 8) |
| Colorless impregnation | Filling of pores or other openings with melted wax, resin, polymer, or plastic to improve appearance and stability. (Colored Stones: Assignment 6) |
| Commercial market | Market sector where average-quality gemstones are used in mass-market jewelry. (Colored Stones: Assignment 7) |
| Conchiolin | The organic "glue" in nacre that holds aragonite platelets together. (Colored Stones: Assignment 16) |
| Conchoidal fracture | A curved and ridged fracture in a gemstone, extending from the surface inward. (Colored Stones: Assignment 3) |
| Consignment | A selection of goods loaned to a dealer by another wholesaler or a gem cutter. (Colored Stones: Assignment 11) |
| Contact metamorphism | 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. (Colored Stones: Assignment 2) |
| Core | The earth's innermost layer. (Colored Stones: Assignment 2) |
| Crazing | The network of tiny fractures that develops when an opal loses moisture. (Colored Stones: Assignment 19) |
| Crown | Top part of the gem above the girdle. (Colored Stones: Assignment 9) |
| Crown-height to pavilion-depth ratio | The relationship of the height of a gem's crown to the depth of its pavilion, judged by viewing its profile. (Colored Stones: Assignment 9) |
| Crust | The surface and outermost layer of the earth. (Colored Stones: Assignment 2) |
| Cryptocrystalline | An aggregate made up of individual crystals detectable only under very high magnification. (Colored Stones: Assignment 3) |
| Crystal structure | Regular, repeating internal arrangement of atoms in a material. (Colored Stones: Assignment 1) |
| Cultured blister pearl | A cultured pearl grown around a nucleus glued under the mantle tissue inside a mollusk's shell. (Colored Stones: Assignment 16) |
| Cultured pearl | A pearl formed as the result of human intervention in the formation process. (Colored Stones: Assignment 16) |
| Custom-made jewelry | A unique piece designed and created for a particular customer, often around specially chosen stones. (Colored Stones: Assignment 7) |
| Cut | A gem dealer's term for a random sample from a parcel of gemstones, often used to assess the parcel's overall quality. (Colored Stones: Assignment 7) |
| Cutter | A manufacturer who produces faceted stones, cabochons, or carvings. (Colored Stones: Assignment 7) |
| Cutting center | A city, region, or country with a large number of gemstone manufacturers. (Colored Stones: Assignment 7) |
| Density | How heavy an object is in relation to its size. (Colored Stones: Assignment 3) |
| Designer cuts | Artistic gem cuts that aren't limited to specific proportions or shapes. (Colored Stones: Assignment 9) |
| Dhun | Smoky corundum that turns blue when treated. (Colored Stones: Assignment 13) |
| Diffraction | A special kind of interference phenomenon that breaks up white light into its spectral hues. (Colored Stones: Assignment 4) |
| Disclosure | Clearly and accurately informing customers about the nature of the goods they buy. (Colored Stones: Assignment 5) |
| Dopstick | Wooden or metal stick that holds the preform during faceting. (Colored Stones: Assignment 9) |
| Double refraction | When a gem's crystal structure splits light into two rays that each travel at a slightly different speed and direction. (Colored Stones: Assignment 4) |
| Doublet | Two separate pieces of material fused or cemented together to form a single assembled stone. (Colored Stones: Assignment 5) |
| Durability | A gemstone's ability to withstand wear, heat, and chemicals. (Colored Stones: Assignment 3) |
| Dyeing | A treatment that adds color or affects color by deepening it, making it more even, or changing it. (Colored Stones: Assignment 6) |
| Eluvial deposit | A deposit where gems are eroded from the source rock but remain in place close to the source. (Colored Stones: Assignment 2) |
| Erosion | The wearing away and transport of rock materials by natural forces. (Colored Stones: Assignment 2) |
| Essence d'orient | A mixture of clear varnish and fish scales used in making imitation pearls. (Colored Stones: Assignment 17) |
| Extinction | Dark areas in a faceted transparent colored stone. (Colored Stones: Assignment 8) |
| Eye-clean | Description for a gem with no inclusions visible to the unaided eye. (Colored Stones: Assignment 10) |
| Facet grade | Gemstone rough that's transparent enough and of high enough quality to produce faceted gems. (Colored Stones: Assignment 7) |
| Faceting head | Device that holds the dopstick at precise angles to allow correct orientation during faceting and polishing. (Colored Stones: Assignment 9) |
| Fantasy cut | A free-form cut that can feature alternating curved and flat surfaces. (Colored Stones: Assignment 9) |
| Feather | A general term for a break in a stone. (Colored Stones: Assignment 10) |
| Fine color | The color or colors in a gemstone's color range considered by the trade to be the most desirable. (Colored Stones: Assignment 8) |
| Fingerprint | Inclusions that form a pattern that often resembles a human fingerprint. (Colored Stones: Assignment 10) |
| Flame fusion | A process in which powdered chemicals are dropped through a high-temperature flame onto a rotating pedestal to produce a synthetic crystal. (Colored Stones: Assignment 5) |
| Floating zone | A melt process where a heating unit passes over a rotating solid rod of chemicals until it forms a synthetic crystal. (Colored Stones: Assignment 5) |
| Fluorescence | Emission of visible light by a material when it's stimulated by ultraviolet radiation. (Colored Stones: Assignment 4) |
| Flux growth | A process in which nutrients dissolve in heated chemicals, then cool to form synthetic crystals. (Colored Stones: Assignment 5) |
| Fracture | Any break in a gem other than cleavage or parting. (Colored Stones: Assignment 3) |
| Fracture (fissure) filling | Using a filler to conceal fractures and improve the apparent clarity of a gem. (Colored Stones: Assignment 6) |
| Free-size | Non-standard cutting, usually applied to large, important stones for use in expensive jewelry where standard size is not a consideration. (Colored Stones: Assignment 7) |
| Full-drilled | Cultured pearl with a hole drilled all the way through; sometimes called drilled-through. (Colored Stones: Assignment 17) |
| Gem species | A broad gem category based on chemical composition and crystal structure. (Colored Stones: Assignment 1) |
| Gem variety | A subcategory of species, based on color, transparency, or phenomenon. (Colored Stones: Assignment 1) |
| Geode | A spherical, often hollow, mineral-lined cavity in rock. (Colored Stones: Assignment 2) |
| Geuda | Milky, grayish, or brownish corundum that can be treated to a fine blue color. (Colored Stones: Assignment 13) |
| Girdle | Narrow section that forms the boundary between the crown and the pavilion, and functions as the gem's setting edge. (Colored Stones: Assignment 9) |
| Goldstone | An imitation of aventurine feldspar made of glass that contains small copper crystals. (Colored Stones: Assignment 26) |
| Gonad | The reproductive organ that produces eggs in females and sperm in males. (Colored Stones: Assignment 16) |
| Grade | A specific rough gemstone quality range, usually determined by color, size, clarity, and price. (Colored Stones: Assignment 7) |
| Graduated strand | A necklace with the largest pearl in the center and progressively smaller pearls approaching the clasp. (Colored Stones: Assignment 16) |
| Grinding | Giving approximate shape to a gemstone, or producing flat planes for polishing facets. (Colored Stones: Assignment 9) |
| Group | A family of gems from several closely related mineral species. (Colored Stones: Assignment 1) |
| Habit | The characteristic external crystal shape or form of a mineral. (Colored Stones: Assignment 3) |
| Half-drilled | Cultured pearl with a hole drilled halfway through to permit mounting on a post. (Colored Stones: Assignment 17) |
| Hank | A number of similar cultured pearl strands bundled together. (Colored Stones: Assignment 16) |
| Hardener | A chemical that treaters mix with some resins to cause them to solidify. (Colored Stones: Assignment 6) |
| Hardness | How well a gemstone resists scratches. Usually expressed in terms of the Mohs scale, with diamond the hardest (10) and talc the softest (1). (Colored Stones: Assignment 3) |
| Hatchery-bred | Describes mollusks bred in laboratory tanks and grown in protected areas rather than collected as adults in the wild. (Colored Stones: Assignment 16) |
| Heat treatment | Exposing a gem to rising temperatures for the purpose of changing its appearance. (Colored Stones: Assignment 6) |
| Heavy minerals | Minerals dense enough to become concentrated and separated from lighter ones by the action of surface water. (Colored Stones: Assignment 2) |
| High grading | In mining terms, theft of a mine's production by its workers. (Colored Stones: Assignment 7) |
| High-end market | Market sector where fine-quality, expensive gemstones are used in unique, handcrafted jewelry pieces. (Colored Stones: Assignment 7) |
| Hollowback | A cabochon with a curved, undercut bottom, designed to lighten the tone of the gem material. (Colored Stones: Assignment 24) |
| Hololith | Gemstone jewelry carved entirely from a single piece of rough. (Colored Stones: Assignment 18) |
| Hue | The first impression of an object's basic color. (Colored Stones: Assignment 8) |
| Hydrothermal fluid | Hot, high-pressure solution that can dissolve, transport, and deposit minerals from one place to another. (Colored Stones: Assignment 2) |
| Hydrothermal growth | A process in which nutrients dissolve in a water solution at high temperature and pressure, then cool to form synthetic crystals. (Colored Stones: Assignment 5) |
| Idiochromatic | A gem colored by an element that is an essential part of its chemical composition. (Colored Stones: Assignment 4) |
| Igneous rock | Rock formed by the crystallization of molten material. (Colored Stones: Assignment 2) |
| Imitation gem | Any material that looks like a natural gem and is used in its place. (Colored Stones: Assignment 5) |
| Imperial | Trade name for finest-quality, semitransparent jadeite with even, vivid green coloration. (Colored Stones: Assignment 18) |
| Imperial topaz | A widely used trade term for gem-quality topaz of medium reddish orange to orange-red color. (Colored Stones: Assignment 22) |
| Included crystal | A mineral crystal trapped within a gem as it grows. (Colored Stones: Assignment 10) |
| Inclusion | A characteristic enclosed within a gemstone, or reaching its surface from the interior. (Colored Stones: Assignment 3) |
| Indicolite | Trade term for blue tourmaline. (Colored Stones: Assignment 23) |
| Inorganic | Composed of, or arising from, non-living matter. (Colored Stones: Assignment 1) |
| Intaglio | A design engraved into the surface of a gemstone. (Colored Stones: Assignment 9) |
| Intended color zoning | Visible face-up color zoning that was planned during the cutting process. (Colored Stones: Assignment 8) |
| Interference | Interaction of two light rays traveling in the same path. (Colored Stones: Assignment 4) |
| Intervalence charge transfer | A process where two impurity atoms separated by another atom can still exchange electrons to selectively absorb light. (Colored Stones: Assignment 4) |
| Intrusion | Large mass of igneous rock that crystallizes underground without reaching the surface. (Colored Stones: Assignment 2) |
| Iridescence | A rainbow effect created when light is broken up into spectral hues by thin layers. (Colored Stones: Assignment 4) |
| Irradiation | Exposing a gem to radiation to change or improve its color. (Colored Stones: Assignment 6) |
| Isomorphous replacement | Substitution of one chemical element for another in the crystal structure of a mineral. (Colored Stones: Assignment 24) |
| Labradorescence | A broad flash of color in labradorite feldspar that disappears when the gem is moved. (Colored Stones: Assignment 4) |
| Lap | Horizontal spinning metal disk used to grind or polish a gem's facets. (Colored Stones: Assignment 9) |
| Lattice diffusion | A treatment in which a gem is exposed to high temperatures and chemicals to allow penetration of color-causing elements. (Colored Stones: Assignment 6) |
| Liquid inclusion | Small pocket in a gem that's filled with fluids and, sometimes, gas bubbles and tiny crystals. Usually created by environmental changes during crystal growth. (Colored Stones: Assignment 3) |
| Lot price | A discounted price for buying an entire parcel or a substantial part of it. (Colored Stones: Assignment 7) |
| Mabe | An assembly composed of a nacre dome, filler, and a mother-of-pearl backing. (Colored Stones: Assignment 16) |
| Magma | General term for any molten rock. (Colored Stones: Assignment 2) |
| Mantle | The organ that lines the mollusk's shell, encloses its soft body, and contains the cells that form pearl sacs and secrete nacre. (Colored Stones: Assignment 16) |
| Mantle convection | Circulation in the mantle that drives the movement of the earth's plates. (Colored Stones: Assignment 2) |
| Mantle-tissue piece | A small square of mantle tissue cut from a donor mollusk and implanted in a host mollusk with or without a bead. (Colored Stones: Assignment 16) |
| Matching tray | A grooved, neutrally colored, non-reflective tray, used to match sets of stones. (Colored Stones: Assignment 11) |
| Matrix | A gem material's host rock, which sometimes becomes part of the finished gem. (Colored Stones: Assignment 19) |
| Melt process | A synthetic-crystal growth method in which the chemical mixture is melted, then recrystallized. (Colored Stones: Assignment 5) |
| Memo | Buying agreement where a dealer entrusts merchandise to a client for inspection and approval without requiring immediate payment. (Colored Stones: Assignment 11) |
| Metamict | A mineral that's been broken down from a crystalline to a partly amorphous state by emanations from radioactive impurities. (Colored Stones: Assignment 23) |
| Metamorphic rock | Rock altered by heat and pressure, or by heated fluids from magma. (Colored Stones: Assignment 2) |
| Metric carat | The international unit of measurement for gem weight (1 carat equals 0.20 gram). (Colored Stones: Assignment 11) |
| Microcrystalline | An aggregate made up of individual crystals visible under magnification. (Colored Stones: Assignment 3) |
| Middle market | Market sector where better-quality gemstones are used in well-finished, moderately priced jewelry pieces. (Colored Stones: Assignment 7) |
| Milk and honey | A two-toned effect seen when a chatoyant gem is positioned at right angles to a light source. (Colored Stones: Assignment 4) |
| Mine lot (mine run) | A mixture of gem qualities that represents unsorted production from a particular mine. (Colored Stones: Assignment 7) |
| Mineral | A natural, inorganic substance with a characteristic chemical composition and usually characteristic structure. (Colored Stones: Assignment 1) |
| Mixed cut | A cutting style that combines brilliant-cut and step-cut facets. (Colored Stones: Assignment 9) |
| Mother-of-pearl | The nacreous layer inside a pearl-bearing mollusk's shell. (Colored Stones: Assignment 16) |
| Mottling | An uneven distribution of color against a contrasting background. (Colored Stones: Assignment 18) |
| Mountain jade | Thick-skinned jadeite boulders. (Colored Stones: Assignment 18) |
| Nacre | The natural substance produced by pearl-bearing mollusks to make pearls. (Colored Stones: Assignment 16) |
| Natural gems | Gems produced by natural processes, without human help. (Colored Stones: Assignment 1) |
| Natural pearl | A pearl that forms without human assistance. (Colored Stones: Assignment 16) |
| Needle | A long, thin inclusion that can be a solid crystal or a hollow tube that might be filled with liquid or gas. (Colored Stones: Assignment 10) |
| Negative crystal | An angular, hollow space within a gem that resembles a mineral inclusion. (Colored Stones: Assignment 10) |
| New mine | The coarsest texture category of jadeite. (Colored Stones: Assignment 18) |
| Old mine | The finest texture category of jadeite. (Colored Stones: Assignment 18) |
| Optic axis | Direction of single refraction in a doubly refractive gem. (Colored Stones: Assignment 4) |
| Organic | Produced by, or derived from, a living organism. (Colored Stones: Assignment 1) |
| Orient | Iridescence seen in some natural and cultured pearls and mother-of-pearl. (Colored Stones: Assignment 4) |
| Origin | The geographical place where a gem was mined. (Colored Stones: Assignment 7) |
| Oxidizing environment | An oxygen-rich environment that surrounds a gem during heat treatment, causing it to absorb oxygen. (Colored Stones: Assignment 6) |
| Paraiba tourmaline | Trade term for rare, expensive, vibrant green to blue or violet elbaite tourmaline, originally found only in Brazil's Paraiba state. (Colored Stones: Assignment 23) |
| Parcel | 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. (Colored Stones: Assignment 7) |
| Parti-colored | Gems that show color zoning with two or more colors. (Colored Stones: Assignment 23) |
| Parting | A flat break in a gemstone caused by concentrated included minerals parallel to a twinning plane. (Colored Stones: Assignment 3) |
| Pavilion | Lower part of a faceted gem below the girdle. (Colored Stones: Assignment 9) |
| Pearl | A nacreous, organic gem formed in the body of a mollusk. (Colored Stones: Assignment 16) |
| Pearl sac | Tissue that encloses an implanted bead nucleus and mantle-tissue piece, or the piece alone, and secretes nacre to form a cultured pearl. (Colored Stones: Assignment 16) |
| Pegmatite | An igneous rock formed 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. (Colored Stones: Assignment 2) |
| Per-carat price | The price of a gem divided by its carat weight. (Colored Stones: Assignment 11) |
| Phenomenon | An unusual optical effect displayed by a gem. (Colored Stones: Assignment 4) |
| Pick price | A premium price for selecting stones from a parcel. (Colored Stones: Assignment 7) |
| Piezoelectricity | A property of some crystals that causes them to vibrate at a constant frequency when subjected to an electrical current. (Colored Stones: Assignment 20) |
| Pinpoint | Minute inclusion enclosed within a gem; can occur singly or in groups called clouds. (Colored Stones: Assignment 10) |
| Placer | Workable alluvial deposit of gem minerals with economic potential. (Colored Stones: Assignment 2) |
| Planned light leakage | Light that exits through a gem's crown in a controlled way due to the correct proportions of its cut. (Colored Stones: Assignment 8) |
| Plate | A section of the earth's rigid outer crust. (Colored Stones: Assignment 2) |
| Plate tectonics | Study of the formation, structure, and movement of the plates of the earth's crust. (Colored Stones: Assignment 2) |
| Play-of-color | The flashing rainbow colors in opal. (Colored Stones: Assignment 4) |
| Pleochroism | When a gem shows different bodycolors from different crystal directions. (Colored Stones: Assignment 4) |
| Pneumatolysis | Crystallization of minerals from a gas. (Colored Stones: Assignment 2) |
| Point | One one-hundredth of a carat (0.01ct.). (Colored Stones: Assignment 11) |
| Polish lines | Tiny, parallel grooves on a facet surface left by the polishing operation. (Colored Stones: Assignment 10) |
| Polishing | Final stage in gem cutting that produces the smoothest possible surface. (Colored Stones: Assignment 9) |
| Polymer | A liquid filling material that's very durable when it dries. (Colored Stones: Assignment 6) |
| Potch opal | Opal that lacks play-of-color. (Colored Stones: Assignment 19) |
| Precious topaz | A trade term for orange-to-yellow and brown topaz. (Colored Stones: Assignment 22) |
| Preform | Rough ground to the approximate shape of the finished stone; also, the act of producing this shape. (Colored Stones: Assignment 9) |
| Primary deposit | Gems found in the rock that carried them to the surface. (Colored Stones: Assignment 2) |
| Process | A procedure that includes cleaning, buffing, and sometimes bleaching, done to make cultured pearls presentable and appealing. (Colored Stones: Assignment 17) |
| Processor | A company that prepares cultured pearls for the market. (Colored Stones: Assignment 16) |
| Proportions | The angles and relative measurements of a polished gem, and the relationships between them. (Colored Stones: Assignment 9) |
| Pulling | A process in which the synthetic crystal grows from a seed that is dipped into a chemical melt, then pulled away as it gathers material. (Colored Stones: Assignment 5) |
| Quench crackling | A rapid heating and cooling process that produces fractures in a stone so it will accept dye. (Colored Stones: Assignment 6) |
| Reconstructed turquoise | A turquoise imitation made of a mixture of powdered minerals, dyed and bonded with plastic or epoxy resin. (Colored Stones: Assignment 25) |
| Reducing environment | An oxygen-poor environment that surrounds a gem during heat treatment, causing it to lose oxygen. (Colored Stones: Assignment 6) |
| Refraction | Change in speed and possible change in direction of light as it travels from one material to another. (Colored Stones: Assignment 4) |
| Regional metamorphism | Changes in rock type and minerals over a wide area, caused by heat and pressure of large-scale geological events. (Colored Stones: Assignment 2) |
| Relatively old mine | The medium texture category of jadeite. (Colored Stones: Assignment 18) |
| Relief | Contrast between an inclusion and its host gem. (Colored Stones: Assignment 10) |
| Resin | A clear, viscous substance that's used to fill fractures in gemstones. (Colored Stones: Assignment 6) |
| Rice pearls | Chinese freshwater cultured pearls shaped and textured like rice grains. (Colored Stones: Assignment 16) |
| River jade | Weathered, thin-skinned jadeite boulders. (Colored Stones: Assignment 18) |
| Rock | A natural material composed of masses of mineral crystals of one or more kinds. (Colored Stones: Assignment 1) |
| Rock cycle | A constant formation and recycling process that creates new rock from old. (Colored Stones: Assignment 2) |
| Rubellite | Trade name for pink to red elbaite tourmaline. (Colored Stones: Assignment 23) |
| Rutilated quartz | A type of sagenitic quartz containing needle-like rutile inclusions. (Colored Stones: Assignment 20) |
| Sagenitic quartz | Transparent quartz, usually rock crystal, that contains eye-visible inclusions, often named according to the type of inclusions it contains. (Colored Stones: Assignment 20) |
| Saturation | A color's strength or intensity. (Colored Stones: Assignment 8) |
| Sawing | Dividing gem rough into easily handled pieces and removing waste areas. (Colored Stones: Assignment 9) |
| Scoop | A small shovel made of thin metal, used for picking up gems. (Colored Stones: Assignment 11) |
| Scratch | A linear scrape, normally seen as a fine, curved or straight, white line. (Colored Stones: Assignment 10) |
| Secondary deposit | Gems found away from their primary source. (Colored Stones: Assignment 2) |
| Sedimentary rock | Rock produced from the eroded and weathered remains of existing rocks. (Colored Stones: Assignment 2) |
| Seed crystal | A tiny crystal used as a template to control the size, speed, or direction of growth and the shape of a growing synthetic crystal. (Colored Stones: Assignment 5) |
| Selective absorption | Process by which a material absorbs some components of visible light and transmits others. (Colored Stones: Assignment 4) |
| Show points | Spots of color near the surface of a jadeite boulder, where the skin is thin enough to allow color to show through. (Colored Stones: Assignment 18) |
| Sieve set | Set of circular plates, each punched with precisely sized holes, used to sort small, round gems by size. (Colored Stones: Assignment 11) |
| Signet | A tablet-cut gem with a flat or slightly domed top and sometimes a carved design, typically set in men's rings and cufflinks. (Colored Stones: Assignment 20) |
| Silicate | A mineral that contains the elements silicon and oxygen. (Colored Stones: Assignment 1) |
| Silk | Group of fine needle-like inclusions. (Colored Stones: Assignment 10) |
| Single refraction | When a gem's crystal structure doesn't change incoming light other than by refraction and absorption. (Colored Stones: Assignment 4) |
| Skull melt | A synthetic-crystal growth method that uses cooling pipes around an interior of melted chemical ingredients. (Colored Stones: Assignment 5) |
| Slocum Stone | An opal imitation made of glass that appeared in the late 1970s. (Colored Stones: Assignment 19) |
| Smoke treatment | Heating a wrapped opal until smoke or ash penetrates its surface to darken it and bring out its play-of-color. (Colored Stones: Assignment 6) |
| Solution process | A growth method in which the synthetic crystal grows from a dissolved chemical mixture, sometimes at high temperature and pressure. (Colored Stones: Assignment 5) |
| Sorting pad | A neutrally colored paper pad on which dealers sort and show gems. (Colored Stones: Assignment 11) |
| Source | A gem-producing area, or a particular mine in that area. (Colored Stones: Assignment 7) |
| Specific gravity (SG) | Ratio of the weight of a material to the weight of an equal volume of water. (Colored Stones: Assignment 3) |
| Spiderweb turquoise | Turquoise that contains matrix in thin, web-like patterns. (Colored Stones: Assignment 25) |
| Spontaneous nucleation | A synthetic-crystal growth method that starts without a seed crystal. (Colored Stones: Assignment 5) |
| Stability | How well a gemstone resists light, heat, and chemicals. (Colored Stones: Assignment 3) |
| Stabilized turquoise | A trade term for polymer-impregnated turquoise. (Colored Stones: Assignment 25) |
| Step cut | Cutting style with mainly square and rectangular facets arranged in concentric rows. (Colored Stones: Assignment 9) |
| Strand | A simple necklace typically composed of pearls; also, pearls very close to the same size strung without a clasp for wholesale marketing. (Colored Stones: Assignment 16) |
| Style | The arrangement of a stone's facets. (Colored Stones: Assignment 9) |
| Subduction | A process that occurs when two of the earth's plates collide, forcing one under the other. (Colored Stones: Assignment 2) |
| Sugar treatment | Soaking an opal in a hot sugar solution and then in sulfuric acid to darken it and bring out its play-of-color. (Colored Stones: Assignment 6) |
| Sun spangles | Circular marks sometimes left in amber when treaters heat and oil it. (Colored Stones: Assignment 27) |
| Surface characteristics | Blemishes or irregularities confined to a pearl's surface. (Colored Stones: Assignment 17) |
| Surface modification | Altering a gem's appearance by applying backings, coatings, or coloring agents like paint. (Colored Stones: Assignment 6) |
| Symmetry | The precision and balance of the corresponding parts of a finished gem. (Colored Stones: Assignment 9) |
| Synthetic gem | A laboratory creation with essentially the same chemical composition, crystal structure, and properties as its natural counterpart. (Colored Stones: Assignment 5) |
| Table facet | Facet at the top of the crown, usually the largest facet on the stone. (Colored Stones: Assignment 9) |
| Thermal shock | Damage caused by sudden, extreme temperature changes. (Colored Stones: Assignment 3) |
| Three-phase inclusion | A hollow cavity in a gem, filled with a liquid, a gas, and one or more crystals. (Colored Stones: Assignment 3) |
| Three-quarter-cut | Cultured pearl with any unsightly portion cut or ground off. (Colored Stones: Assignment 17) |
| Tone | Degree of darkness or lightness of a color. (Colored Stones: Assignment 8) |
| Toughness | How well a gemstone resists breaking and chipping. (Colored Stones: Assignment 3) |
| Tourmalinated quartz | A type of sagenitic quartz containing needle-like or rod-like tourmaline inclusions. (Colored Stones: Assignment 20) |
| Trace elements | Atoms in a gem that aren't part of its essential chemical composition. (Colored Stones: Assignment 3) |
| Trade terms | Terms often used in the jewelry industry to describe particular gemstone colors or link gems with specific geographic locations. (Colored Stones: Assignment 8) |
| Transition elements | Elements that can selectively absorb some wavelengths of visible light and produce color in gems. (Colored Stones: Assignment 4) |
| Treatment | Any human-controlled process, beyond cutting and polishing, that improves the appearance, durability, or value of a gem. (Colored Stones: Assignment 6) |
| Triplet | A single assembled stone made from three separate pieces of material fused or cemented together, or from two pieces and a colored cement layer. (Colored Stones: Assignment 5) |
| Twinning | Change in a gem's crystal direction during or after growth. (Colored Stones: Assignment 3) |
| Two-phase inclusion | A hollow cavity in a gem, usually filled with a liquid and a gas. (Colored Stones: Assignment 3) |
| Type A jadeite | Natural jadeite enhanced only with a surface coating of wax. (Colored Stones: Assignment 18) |
| Type B jadeite | Natural jadeite that's bleached in acid to remove undesirable staining, then impregnated with wax or polymers. (Colored Stones: Assignment 18) |
| Type C jadeite | Natural jadeite that's dyed and often bleached and impregnated with wax or polymers. (Colored Stones: Assignment 18) |
| Uniform strand | A necklace featuring pearls that are very nearly the same size. (Colored Stones: Assignment 16) |
| Unintended color zoning | Visible face-up color zoning that the cutter was unable to conceal. (Colored Stones: Assignment 8) |
| Unit cell | The smallest group of atoms with both the characteristic chemical composition and crystal structure of a mineral. (Colored Stones: Assignment 3) |
| Unit price | The price per piece. (Colored Stones: Assignment 11) |
| Unplanned light leakage | Light that exits through the pavilion in an uncontrolled way due to compromises in a gem's proportions. (Colored Stones: Assignment 8) |
| Value factors | Features used to judge the quality and value of pearls. (Colored Stones: Assignment 17) |
| Vein | A mineral deposit that occupies an existing fissure or fracture in the rock. (Colored Stones: Assignment 2) |
| Volcanic | Pertaining to igneous activity at the earth's surface, where magma erupts through a volcano or a fissure. (Colored Stones: Assignment 2) |
| Watermelon tourmaline | A tourmaline, usually elbaite, with color zoning made up of a pink central zone surrounded by a green overgrowth. (Colored Stones: Assignment 23) |
| Wholesaler | A company or individual that supplies gems to jewelry manufacturers and retailers. (Colored Stones: Assignment 7) |
| Window | An area of weak saturation in a transparent gemstone's bodycolor that usually results from the way the gem was cut. (Colored Stones: Assignment 8) |
| Xenocryst | A "foreign crystal" that formed in unrelated rocks and was brought to the surface as a passenger in magma. (Colored Stones: Assignment 2) |
Created by:
mathewsjp6823