Gemstone Words and Terms Glossary

Jewelry consumers are often bombarded by technical, scientific and jewelry-trade phrases when shopping for that special piece of jewelry.

Below are many of the words and phrases used when discussing gemstones.

The appearance of a floating, billowy light in cabochon gemstonesor a stationary sheen on the flat surface of a gemstone. Seen incertain Feldspars such as Moonstone. Schiller.

Altered Stone
Any stone that has been changed in appearance,particularly in color, by an artificial process. Also referred toas an Enhanced Gemstone or a Treated Gemstone. Heating,irradiation, and dyeing are among the processes used to changegemstone appearance.

The color violet to purple in gemstones.

Angle of Incidence
The angle at which a ray of light enters a stone asmeasured from normal.

Angle of Reflection
The angle at which a reflected ray of light leaves asurface as measured from normal.

Angle of Refraction
The angle at which a reflected ray of light leaves asurface as measured from normal.

Term used in gemology for double refraction.

Artificial Stone
A man-made, imitation or synthetic gem.

The appearance of a rayed figure or rayed star in agemstone, caused by the reflection of light from minuteinclusions. Star Sapphires and Star Rubies are two well-knownexamples of gemstones featuring a rayed star.

A glittery appearance of the surface of a gemstone,caused by the reflection of light off small mineral inclusions.Aventurine Quartz and Goldstone (glass) both have aventurescence.

Balas Ruby
Trade name for Red Spinel.

May apply to certain gemstones or pearls. Either agemstone or pearl with an irregular shape, such as Tumbled Stonesor Baroque Pearls.

The portion of a facetted gemstone below the Girdle.Also known as the Pavilion.

The English name for the Baguette cut.

Bead Setting
A method of securing a facetted stone. A small burr ofmetal is raised with a graver and worked to the edge of the stone.This burr is then burnished with a concave tipped punch into asmall ball over the girdle of the stone. Normally used to securevery small gemstones, usually in multiples.

The supporting ledge of a stone setting.

A thin strip of metal that holds a gemstone in place.Used in place of prongs.

A double-refractive gemstone, which has two directionsof single refraction or optic axes.

The numerical measurement of double refraction ingemstones.

The process of placing the facets on a stone.

Body Appearance
The optical characteristic of a gem produced by internalinclusions, fractures or layers.

Body Color
The dominant hue within a gemstone.

Box Setting
A method of stone setting in which the gem is enclosedin a box and the edges of the metal are pressed down to securethe stone.

The total amount of white light returned to the viewerby a gem. This includes internal and external reflections.

Bristol Stone/Bristol Diamond
Old trade-term for colorless crystal quartz. Also atrade name for colored glass imitations, Bristol Glass orBristows.

A method of rough-diamond fashioning by rubbing onediamond against another.

A gemstone with an unfacetted domed form. The oldestform of gem cutting.

Calibre Cut
Gemstones cut to a specific, standardized size formounting. Also, small gem material cut for pave' setting.

A gem or shell material--usually with two or moredistinct colored layers. The top layer is carved in relief andthe bottom layer acts as a contrasting background.

A unit of weight measure for gems.

Change of Color
A phenomenon seen in some gems which have a differentcolor in natural light than in artificial light. The color-changeis caused by selective absorption and transmission of light.Alexandrite has become a very well known color-change gem, butother gemstones may exhibit the phenomenon.

The appearance of well-defined bands or threads of lightacross the surface of a gemstone. This appearance is caused bythe reflection of light off small parallel mineral inclusions.May appear as a single-band chatoyancy--Cat's Eye--or a series ofbands--Tiger's Eye.

The tendency of Opals to crack when exposed to heat ordrying air. Also known as Crazing.

A gemstone with a smooth concave depression.

A popular, common name for a small rose-cut or single-cutgemstone.

Claw Setting
A stone setting of projecting metal claws which grip thestone at--and just above--the girdle.

A trade term for gemstones which are free of noticeableflaws.

A smooth, flat break or separation in a gem along thedirection of its atomic structure.

A group of small, white inclusions that give a cloudyappearance to a diamond.

Cluster Setting
Closely set gemstones arranged to give the illusion of asingle, larger gemstone.

Coated Stone
A gemstone covered by an artificially appliedtransparent material to enhance its color. Often used with Topaz.

Collet Set
A variation on box setting in which the sides of the boxare filed away to sallow more light to enter the gemstone.

Color Zoning
Uneven color in gemstones in irregular patches. Can beeither different colors or different tones of the same color.

Colored Stones
A gemstone other than a diamond.

The tendency of Opals to crack when exposed to heat ordrying air. Also known as Checking.

Critical Angle
Greatest angle measured from normal at which light canbe refracted out of a stone. Small angle at which light istotally internally reflected.

The part of a facetted gemstone above the girdle.

Crown Setting
A collet setting consisting off a flared cylinder withone end of the cylinder notched to form prongs.

Extremely small crystals which cannot be seenseparately, even under high magnification.

A solid made up of atoms, bounded by natural planarsurfaces.

Crystal System
The classification of minerals according to thegeometric form in which their crystals grow. Each mineral has adistinct system--Isometric, Tetragonal, Hexagonal, Orthorhombic,Monoclinic and Triclinic.

Having a regular crystal structure.

The science of the internal structure of crystals.

Cubic System
The Isometric crystal system which consists of threeaxes, each of equal length and perpendicular to others.

A small polished surface placed at what would be thepoint or ridge of a facetted stone, used to reduce chipping.

The specific from into which a stone is fashioned. Oneof the deciding factors in gemstone value.

A raised relief carved into a gemstone in a concavedepression.

Mass per unit volume. The amount of matter in a givenspace. The higher density/atomic mass of a gemstone, the more itweighs for a given size.

An early term for glass imitation stone without foilbacking.

The transmission of two different colors in twodifferent optical planes as light passes through a gemstone. Maybe used as a method of distinguishing one type of gemstone fromanother.

An instrument used to view the light passing through agemstone to determine the presence of dichroism.

The separation of light into its spectral colors as itpasses through a gemstone.

A twelve-sided geometric solid. One of the crystal formsfound in the Isometric crystal system.

Double Refraction
The separation of a beam of light into two separatebeams as it enters a gemstone. The two beams travel at differentspeeds. May be used to distinguish one gemstone material fromanother. Occurs in all crystal systems except Isometric.

An assembled stone of two parts. Colorless cement orheat is used to join the parts together. Often used with Opals.

The combined characteristics of hardness, toughness andstability in gemstones. One of the deciding factors in gemstonevalue.

Dyed Stone
A gemstone to which an artificial stain is added toimprove color or to imitate a more valuable gemstone.

The plane surfaces which form the sides of a crystal.

A planar surface which is polished onto a gemstone.

Fancy Cut/Fancy Shape
Any style of gemstone cutting other than the roundbrilliant or single cut.

Fancy Diamond
Any diamond with a body color strong enough to beattractive.

A trade term referring to any inclusion within a gem,usually a jagged irregular fracture which appears white.

Fingerprint Inclusion
Liquid and/or gas or solid flaws in gemstones whichalign in the form of a human fingerprint.

The quality of a prepared surface. In facettedgemstones, the placing of the facets and the quality of polish.In cabochon gemstones, the quality of the polish.

The play of color on or within a gemstone as a result ofdispersion. Prominent valued feature of Opals and Fire Agates.

Any visible imperfection within a gemstone.

The emission of visible light when a gemstone is exposedto ultraviolet light. Used a method of distinguishing onegemstone from another and a natural gemstone from a syntheticgemstone.

Foil Backed
The adding of a layer of metallic foil to the back of agemstone to improve its color or brilliancy.

A break or chip in a gemstone in any direction otherthan along a cleavage plane.

A cut and polished stone which possesses the beauty,durability and rarity necessary for use in jewelry.

The study of gemstones--identification, grading,appraisal, marketing, and fashioning.

A rock which contains a cavity lined with quartz orother gemstone crystals.

A gemstone with a glowing, milky sheen that moves as thestone is moved in the path of a light source. Opalescence.

The outer edge of a gemstone.

The art of engraving or carving gems.

Two or more chemically related gemstone materials,similar in structure and physical properties.

Gypsy Setting
A setting in which the crown of a gem is the onlyportion exposed and the table of the gemstone is nearly levelwith the surrounding metal. No prongs or separate bezel isevident; all means of setting the gemstone are below the metal'ssurface.

The most common form in which a mineral occurs.

A gemstone material's ability to resist scratching.

An added finding to secure a gemstone in a prong setting.

Heating a gemstone material to improve color.

Heavy Liquid
A liquid of known specific gravity, used to test thespecific gravity of a gemstone.

Hexagonal System
A crystal system which consists of four axes, threeintersect at a 60-degree angle of each other while the fourth isperpendicular to the other three.

Hollowed Cab
A cabochon hollowed from the back. Technique is sued tolighten the color of the stone.

Illusion Setting
A setting in which the surrounding metal's surface iscut or shaped to appear to be part of the gemstone. Technique isoften used to enhance the perceived size of small diamonds.

A visible irregularity in a gemstone.

A design carved into the surface of a gemstone--theopposite in character of a cameo.

The color of a gemstone from bright to dull.

Interference Colors
Colors revealed by a polarisope as polarized light passthrough a gemstone. Used to detect the presence of doublerefractivity in a gemstone.

Spectral colors observed inside or on a gemstone. It iscaused by light passing through layers of differing refractiveindexes. The colors seen in Opals are a result of iridescence.

Isometric System
The Cubic crystal system which consists of three axes,each of equal length and perpendicular to others.

Man-made gemstone that has nearly the same physical,optical and chemical properties of a natural gemstone. Syntheticgemstone.

The appearance of a surface resulting from reflectedlight. Diamonds exhibit Adamantine Luster, glass and mostgemstones exhibit Vitreous Luster, amber exhibits Resinous Luster.

A trade term referring to the quality of a gemstone'scut.

The rock in which gemstone material is found. Somematrix material may remain in a finished gemstone--the veining inturquoise is a common matrix seen in a finished gemstone.

Gemstones of approximately .18 carats or less. May referto all gemstones or cutting styles, but is usually used forround, facetted diamonds.

A style of setting in which the stone is held in placeby a row of tiny beads along the girdle of the stone.

Inorganic substances occurring naturally and having adefinite chemical composition and crystal structure.

The study of minerals, including their physical andchemical properties.

Mixed Cut
A gemstone cut consisting of a brilliant-cut crown andstep-cut pavilion.

Moh’s Scale
A categorization of minerals according to their hardness--resistanceto scratching. Diamond is the hardest and talc is the softest.

Monoclinic System
A crystal system which consists of three axes, eachunequal in length with two intersecting at oblique angles and thethird perpendicular to the other two.

The portion of a piece of jewelry which holds a gemstone.

In the study of light, an imaginary line perpendicularto a surface. Used in gemology to describe the angle at whichlight strikes an object.

An eight-sided geometric solid and one of the forms inthe Isometric Crystal System. The most common crystal in whichdiamonds occur.

Milky or pearly appearance. Girasol.

The quality of not allowing the transmission of light.

Optic Character
The effect a material has on the transmission on light.

Optical Properties
The behavior of light within a material.

Organic Gem
Naturally occurring substances wholly or partly derivedfrom plants or animals--coral, jet, pearls.

Oriented Stone
A gemstone cut to place the optical axis, and resultingphenomenon, in proper position--star sapphires and star rubies.

Orthorhombic System
A crystal system which consists of three axes, eachunequal in length and intersecting at ninety-degree angles.

Flat, smooth breakage of a mineral along planes ortwinning, commonly found in corundum.

Glass usually containing lead oxide and cut to simulatea gemstone.

Small stones set in the surface of metal as closetogether as possible.

The portion of a facetted gemstone below the girdle.

An optical effect which appears in certain gemstonematerials. Often revealed by or enhanced by proper fashioning.

A continuing glow exhibited by some gemstones after thesource of illumination has been removed.

Play of Color
Prismatic flashes of color seen within a gemstone. Thecolor display in Opal.

Change of colors observed in double-refractive gemstoneswhen viewed different directions. Selective absorption andvarying transmission rates of light cause the color change whenthe gemstone is viewed along different optical axes.

A narrow tab of metal folded over the girdle of agemstone to secure it in a setting.

Reconstructed Stone
A man-made gemstone produced by fusing together smallparticles of a natural stone.

Light returned to the viewer after striking a surface withoutentering it.

The change of velocity and resulting bending of light asit passes from one medium into another medium of differentoptical character.

Refractive Index
The ratio of speed of light in air to its speed within asubstance.

An instrument used to measure the degree of refractionwith a gemstone. One of the primary tests to identify gemstonematerial.

Small, jeweled or facetted beads often used as spacersin a string.

Uncut or unfashioned gemstone material.

A gemstone cut in the form of a beetle.

The appearance of a floating, billowy light in cabochongemstones or a stationary sheen on the flat surface of a stone.Seen in certain Feldspars such as Moonstone. Adularescence.

Reflections from a polished surface as its relativeposition to either the viewer or the source of illuminationchanges.

Carved or engraved ivory or vegetable ivory. Theengraved lines and textured surfaces are often colored with inksand dyes.

A mounting or the portion of a mounting which actuallyholds the stone.

The ability of a gemstone to resist deterioration.

Star Stone
A gemstone in which the phenomenon of asterism isvisible.

Irregularity in the ordered structure of the atoms in acrystal.

Glass containing a high amount of lead oxide and cut tosimulate a gemstone. Named for its inventor Josef Strass.

A substance used to imitate a more valuable gemstone.The substitute substance may be natural or man-made.

A man-made gemstone that has nearly the same physical,optical and chemical properties of a natural gemstone. Lab-growngemstone.

The horizontal flat surface on the crown of a facettedgemstone.

Tetragonal System
A crystal system which consists of three axes, two ofequal length and perpendicular to one another, the thirdperpendicular to the plane of the others.

Tiffany Setting
A solitaire (single-stone) setting for a facetted stoneconsisting of six long, slender prongs.

The relative lightness or darkness of a color.

A substance that allows transmitted light to clearlypass through. Objects cannot be seen through a translucentsubstance.

A substance that allows transmitted light to clearlypass through. Objects can be seen through a transparent substance.

The transmission of three different colors in threedifferent optical planes as light passes through a gemstonematerial. May be used to distinguish one gemstone material fromothers.

Triclinic System
A crystal system which consists of three axes, all ofunequal lengths and at oblique angles to each other.

A twenty-four sided geometric solid. One of the crystalforms of the Isometric crystal system.

Tube Setting
A bezel setting in which a bearing cut into the end of atube.

Tulip Setting
A prong setting with a small base where it is attachedto the body of the jewelry piece and usually has a peg on thebase which is inserted into a hole for solder attachment.

Tumbled Stone
A gem with an irregular or baroque shape. Polished byrandom application of an abrasive material.

Uniaxial Stone
A gemstone possessing one optical axis. Crystals of thehexagonal or tetragonal system are uniaxial.

Vegetable Ivory
Any hard, white or cream-colored product of a plant whichsimulates elephant ivory. It has gained in popularity as theharvesting of animal has been banned or severely limited.