Glossary: Colored Gems

  • A


    The cloudy bluish white light in a moonstone, caused by scattering of light.


    Lacking a regular crystal structure.


    Crossing of chatoyant bands, creating a star in the dome of a cabochon.


    A glittery effect caused by light reflecting from small, flat inclusions within a gemstone.

  • B


    Characteristic or irregularity confined to the surface of a polished gemstone.


    A gemstone's basic color, determined by its selective absorption of light.

    Brilliant Cut

    Cutting style with triangular or kite-shaped facets that radiate from the center toward the girdle.

  • C


    A smoothly rounded polished gem with a domed top and a flat or curved base.

    Calibrated Sizes

    Gemstone sizes cut to fit standard mountings.


    A gem carving style in which the design, often a woman's profile, projects slightly from a flat or curved surface.

    Cavity Filling

    Treatment that fills and seals voids to improve appearance and add weight.


    Bands of light in certain gems, caused by reflection of light from many parallel, needle-like inclusions or hollow tubes.


    A gemstone's relative freedom from inclusions and blemishes.

    Clarity Characteristic

    Internal or external feature of a gemstone that helps determine its quality.


    A smooth, flat break in a gemstone parallel to planes of atomic weakness.

    Color Center

    A small defect in the atomic structure of a material that can absorb light and give rise to a color.

    Color Change

    A distinct change in gem color under different types of lighting.

    Color Range

    The selection of colors in which a gemstone occurs.

    Color Zoning

    Areas of different color in a gem, caused by variations in growth conditions.

    Colored Stone

    Any gem material other than diamond.

    Colorless Impregnation

    Filling of pores or other openings with melted wax, resin, polymer, or plastic to improve appearance and stability.

    Commercial Market

    Market sector where average-quality gemstones are used in mass-market jewelry.

    Conchoidal Fracture

    A curved and ridged fracture in a gemstone, extending from the surface inward.


    The network of tiny fractures that develops when an opal loses moisture.

    Crystal Structure

    Regular, repeating internal arrangement of atoms in a material.

    Cutting Center

    A city, region, or country with a large number of gemstone manufacturers.

  • D


    The weight of an object in relation to its size.

    Designer Cuts

    Artistic gem cuts that aren't limited to specific proportions or shapes.


    The separation of white light into spectral colors.


    Two separate pieces of material fused or cemented together to form a single assembled stone.


    A gemstone's ability to withstand wear, heat, and chemicals.


    A treatment that adds color or affects color by deepening it, making it more even, or changing it.

  • E


    Dark areas in a faceted transparent colored stone.


    Description for a gem with inclusions visible only under magnification.

  • F


    A flat, polished surface on a finished gem.

    Fancy Shape

    Any gemstone shape other than round.

    Fantasy Cut

    A free-form cut that can feature alternating curved and flat surfaces.

    Fashion Jewelry

    Inexpensive, or "costume," jewelry, often composed of materials other than precious metals and gemstones.


    Another term for gem cutting and polishing.


    A general term for a break in a stone.


    A characteristic or part of a piece of jewelry.

    Federal Trade Commission (FTC)

    A US Government agency that issues guidelines for the jewelry trade.


    Small components used to make or repair jewelry.

    Fine Color

    The color or colors in a gemstone's color range considered by the trade to be the most desirable.


    The quality of the polish and precision of the cut of a fashioned gemstone.

    Flame Fusion

    A process in which powdered chemicals are dropped through a high-temperature flame onto a rotating pedestal to produce a synthetic crystal.

    Fluid Inclusion

    Small pocket in a gem that's filled with fluids and, sometimes, gas bubbles and tiny crystals.


    Emission of visible light by a material when it's stimulated by ultraviolet radiation.

    Flux Growth

    A process in which nutrients dissolve in heated chemicals, then cool to form synthetic crystals.


    Any break in a gem other than cleavage or parting.

    Fracture (Fissure) Filling

    Using a filler to conceal fractures and improve the apparent clarity of a gem.

  • G

    Gem Species

    A broad gem category based on chemical composition and crystal structure.

    Gem Variety

    A subcategory of species, based on color, transparency, or phenomenon.


    A family of gems from several closely related mineral species.

    Guild Store

    Any jewelry store that specializes in high-end goods.

  • H


    How well a gemstone resists scratches and abrasion.

    Heat Treatment

    Exposing a gem to rising temperatures for the purpose of changing its appearance.


    The first impression of an object's basic color.

    Hydrothermal Growth

    A process in which nutrients dissolve in a water solution at high temperature and pressure, then cool to form synthetic crystals.

  • I

    Included Crystal

    A mineral crystal trapped within a gem as it grows.


    A characteristic enclosed within a gemstone or reaching its surface from the interior.


    Composed of, or arising from, non-living matter.


    A design engraved into the surface of a gemstone.


    A rainbow effect created when light is broken up into spectral hues by thin layers.


    Exposing a gem to radiation to change or improve its color.

  • L


    A broad flash of color in labradorite feldspar that disappears when the gem is moved.

    Lattice Diffusion

    Exposing a gem to high temperatures and chemicals to allow penetration of color-causing elements.


    The appearance of a material's surface in reflected light.

  • M

    Metric Carat

    The international unit of measurement for gem weight (1 carat equals 0.20 gram).

    Milk & Honey

    A two-toned effect seen when a chatoyant gem is positioned at right angles to a light source.

    Mixed Cut

    A cutting style that combines brilliant-cut and step-cut facets.

  • N

    Natural Gems

    Gems produced by natural processes, without human help.

  • O


    Iridescence seen in some natural and cultured pearls and mother-of-pearl.

  • P


    A rare pinkish orange sapphire.


    A flat break in a gemstone parallel to a twinning plane.

    Per-Carat Price

    The price of a gem divided by its carat weight.


    An unusual optical effect displayed by a gem.


    The flashing rainbow colors in opal.


    When a gem shows different bodycolors from different directions.


    One one-hundredth of a carat (0.01 ct.).


    The angles and relative measurements of a polished gem, and the relationships between them.


    A historical record of ownership or origin for a gem or piece of jewelry.


    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.

  • Q

    Quench Crackling

    A rapid heating and cooling process that produces fractures in a stone so it will accept dye.

  • S


    A color's strength or intensity.


    Flashes of light displayed by a polished gemstone when the gem, the observer, or the light source moves.

    Selective Absorption

    Process by which a material absorbs some components of visible light and returns others.


    The part of a ring that encircles the finger.


    The face-up outline of a gem.


    Group of fine, needle-like inclusions.

    Smoke Treatment

    Heating a wrapped opal until smoke or ash penetrates its surface to darken it and bring out its play-of-color.


    A gem-producing area, or a particular mine in that area.

    Specific Gravity

    Ratio of the weight of a material to the weight of an equal volume of water.


    How well a gemstone resists the effects of light, heat, and chemicals.

    Steam Cleaner

    A machine that cleans jewelry with high-pressure steam.

    Step Cut

    Cutting style with mainly square and rectangular facets arranged in concentric rows.

    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.

    Surface Modification

    Altering a gem's appearance by applying backings, coatings, or coloring agents like paint.

    Synthetic Gem

    A laboratory creation with essentially the same chemical composition, crystal structure, and properties as its natural counterpart.

  • T


    Restatement of a benefit, posed as a question and designed to elicit agreement.


    A two-part sales technique that removes a customer's "just looking" defense.


    A procedure for receiving customer jewelry for repair, appraisal, or cleaning.

    Thermal Shock

    Damage caused by sudden, extreme temperature changes.


    Degree of darkness or lightness of a color.

    Total Gem Weight

    The combined weight of all the stones in a piece of jewelry that contains a variety of gems.


    How well a gemstone resists breaking, chipping, and cracking.

    Trace Elements

    Atoms in a gem that aren't part of its essential chemical composition.

    Trade Terms

    Terms often used in the jewelry industry to describe particular gemstone colors or link gems with specific geographic locations.


    Degree to which a material allows light to pass through it.


    Any human-controlled process, beyond cutting and polishing, that improves the appearance, durability, or value of a gem.


    The part of the add-on close that requires the customer to make a "yes" or "no" decision.


    A single assembled stone made from three separate pieces of material fused or cemented together, or from two pieces and a colored cement layer.

    Twinning Plane

    Location of a change of direction in a gemstone's crystal structure during growth.

  • U

    Ultrasonic Cleaner

    A machine that cleans jewelry with high-frequency sound waves in a liquid solution.

  • W


    An area of weak saturation in a transparent gemstone's bodycolor that usually results from the way the gem was cut.