Adularescence

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

Amorphous

Lacking a regular crystal structure.

Asterism

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

Aventurescence

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

Blemish

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

Bodycolor

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.

Cabochon

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

Calibrated Sizes

Gemstone sizes cut to fit standard mountings.

Cameo

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.

Chatoyancy

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

Clarity

A gemstone's relative freedom from inclusions and blemishes.

Clarity Characteristic

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

Cleavage

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.

Crazing

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.

Density

The weight of an object in relation to its size.

Designer Cuts

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

Dispersion

The separation of white light into spectral colors.

Doublet

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

Durability

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

Dyeing

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

Extinction

Dark areas in a faceted transparent colored stone.

Eye-Clean

Description for a gem with inclusions visible only under magnification.

Facet

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.

Fashioning

Another term for gem cutting and polishing.

Feather

A general term for a break in a stone.

Feature

A characteristic or part of a piece of jewelry.

Federal Trade Commission (FTC)

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

Findings

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.

Finish

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.

Fluorescence

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.

Fracture

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.

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.

Group

A family of gems from several closely related mineral species.

Guild Store

Any jewelry store that specializes in high-end goods.

Hardness

How well a gemstone resists scratches and abrasion.

Heat Treatment

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

Hue

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.

Included Crystal

A mineral crystal trapped within a gem as it grows.

Inclusion

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

Inorganic

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

Intaglio

A design engraved into the surface of a gemstone.

Iridescence

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

Irradiation

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

Labradorescence

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.

Luster

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

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.

Natural Gems

Gems produced by natural processes, without human help.

Orient

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

Padparadscha

A rare pinkish orange sapphire.

Parting

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

Per-Carat Price

The price of a gem divided by its carat weight.

Phenomenon

An unusual optical effect displayed by a gem.

Play-Of-Color

The flashing rainbow colors in opal.

Pleochroism

When a gem shows different bodycolors from different directions.

Point

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

Proportions

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

Provenance

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

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.

Quench Crackling

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

Saturation

A color's strength or intensity.

Scintillation

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.

Shank

The part of a ring that encircles the finger.

Shape

The face-up outline of a gem.

Silk

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.

Source

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.

Stability

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.

Tag

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

Take-Away

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

Take-In

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

Thermal Shock

Damage caused by sudden, extreme temperature changes.

Tone

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.

Toughness

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.

Transparency

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

Treatment

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

Trigger

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

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.

Twinning Plane

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

Ultrasonic Cleaner

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

Window

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