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.

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

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

Amethystine
The color violet to purple in gemstones.

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

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

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

Anisotropic
Term used in gemology for double refraction.

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

Asterism
The appearance of a rayed figure or rayed star in a gemstone, caused by the reflection of light from minute inclusions. Star Sapphires and Star Rubies are two well-known examples of gemstones featuring a rayed star.

Aventurescence
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.

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

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

Baton
The English name for the Baguette cut.

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

Bearing
The supporting ledge of a stone setting.

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

Biaxial
A double-refractive gemstone, which has two directions of single refraction or optic axes.

Birefringence
The numerical measurement of double refraction in gemstones.

Blocking
The process of placing the facets on a stone.

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

Body Color
The dominant hue within a gemstone.

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

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

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

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

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

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

Cameo
A gem or shell material--usually with two or more distinct colored layers. The top layer is carved in relief and the bottom layer acts as a contrasting background.

Carat
A unit of weight measure for gems.

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

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

Checking
The tendency of Opals to crack when exposed to heat or drying air. Also known as Crazing.

Chevee
A gemstone with a smooth concave depression.

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

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

Clean
A trade term for gemstones which are free of noticeable flaws.

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

Cloud/Cloudy
A group of small, white inclusions that give a cloudy appearance to a diamond.

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

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

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

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

Colored Stones
A gemstone other than a diamond.

Crazing
The tendency of Opals to crack when exposed to heat or drying air. Also known as Checking.

Critical Angle
Greatest angle measured from normal at which light can be refracted out of a stone. Small angle at which light is totally internally reflected.

Crown
The part of a facetted gemstone above the girdle.

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

Cryptocrystalline
Extremely small crystals which cannot be seen separately, even under high magnification.

Crystal
A solid made up of atoms, bounded by natural planar surfaces.

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

Crystalline
Having a regular crystal structure.

Crystallography
The science of the internal structure of crystals.

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

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

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

Cuvette
A raised relief carved into a gemstone in a concave depression.

Density
Mass per unit volume. The amount of matter in a given space. The higher density/atomic mass of a gemstone, the more it weighs for a given size.

Dentelles
An early term for glass imitation stone without foil backing.

Dichroism
The transmission of two different colors in two different optical planes as light passes through a gemstone. May be used as a method of distinguishing one type of gemstone from another.

Dichroscope
An instrument used to view the light passing through a gemstone to determine the presence of dichroism.

Dispersion
The separation of light into its spectral colors as it passes through a gemstone.

Dodecahedron
A twelve-sided geometric solid. One of the crystal forms found in the Isometric crystal system.

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

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

Durability
The combined characteristics of hardness, toughness and stability in gemstones. One of the deciding factors in gemstone value.

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

Face
The plane surfaces which form the sides of a crystal.

Facet
A planar surface which is polished onto a gemstone.

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

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

Feather
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 which align in the form of a human fingerprint.

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

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

Flaw
Any visible imperfection within a gemstone.

Fluorescence
The emission of visible light when a gemstone is exposed to ultraviolet light. Used a method of distinguishing one gemstone from another and a natural gemstone from a synthetic gemstone.

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

Fracture
A break or chip in a gemstone in any direction other than along a cleavage plane.

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

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

Geode
A rock which contains a cavity lined with quartz or other gemstone crystals.

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

Girdle
The outer edge of a gemstone.

Glyptic
The art of engraving or carving gems.

Group
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 only portion exposed and the table of the gemstone is nearly level with the surrounding metal. No prongs or separate bezel is evident; all means of setting the gemstone are below the metal's surface.

Habit
The most common form in which a mineral occurs.

Hardness
A gemstone material's ability to resist scratching.

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

Heat-Treatment
Heating a gemstone material to improve color.

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

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

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

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

Inclusion
A visible irregularity in a gemstone.

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

Intensity
The color of a gemstone from bright to dull.

Interference Colors
Colors revealed by a polarisope as polarized light pass through a gemstone. Used to detect the presence of double refractivity in a gemstone.

Iridescence
Spectral colors observed inside or on a gemstone. It is caused by light passing through layers of differing refractive indexes. 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.

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

Luster
The appearance of a surface resulting from reflected light. Diamonds exhibit Adamantine Luster, glass and most gemstones exhibit Vitreous Luster, amber exhibits Resinous Luster.

Make
A trade term referring to the quality of a gemstone's cut.

Matrix
The rock in which gemstone material is found. Some matrix material may remain in a finished gemstone--the veining in turquoise is a common matrix seen in a finished gemstone.

Melee
Gemstones of approximately .18 carats or less. May refer to all gemstones or cutting styles, but is usually used for round, facetted diamonds.

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

Mineral
Inorganic substances occurring naturally and having a definite chemical composition and crystal structure.

Mineralogy
The study of minerals, including their physical and chemical properties.

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

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

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

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

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

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

Opalescence
Milky or pearly appearance. Girasol.

Opaque
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 derived from plants or animals--coral, jet, pearls.

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

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

Parting
Flat, smooth breakage of a mineral along planes or twinning, commonly found in corundum.

Paste
Glass usually containing lead oxide and cut to simulate a gemstone.

Pave'
Small stones set in the surface of metal as close together as possible.

Pavilion
The portion of a facetted gemstone below the girdle.

Phenomenon
An optical effect which appears in certain gemstone materials. Often revealed by or enhanced by proper fashioning.

Phosphorescence
A continuing glow exhibited by some gemstones after the source of illumination has been removed.

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

Pleochroism
Change of colors observed in double-refractive gemstones when viewed different directions. Selective absorption and varying transmission rates of light cause the color change when the gemstone is viewed along different optical axes.

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

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

Reflection
Light returned to the viewer after striking a surface without entering it.

Refraction
The change of velocity and resulting bending of light as it passes from one medium into another medium of different optical character.

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

Refractometer
An instrument used to measure the degree of refraction with a gemstone. One of the primary tests to identify gemstone material.

Rondelles
Small, jeweled or facetted beads often used as spacers in a string.

Rough
Uncut or unfashioned gemstone material.

Scarab
A gemstone cut in the form of a beetle.

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

Scintillation
Reflections from a polished surface as its relative position to either the viewer or the source of illumination changes.

Scrimshaw
Carved or engraved ivory or vegetable ivory. The engraved lines and textured surfaces are often colored with inks and dyes.

Setting
A mounting or the portion of a mounting which actually holds the stone.

Stability
The ability of a gemstone to resist deterioration.

Star Stone
A gemstone in which the phenomenon of asterism is visible.

Strain
Irregularity in the ordered structure of the atoms in a crystal.

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

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

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

Table
The horizontal flat surface on the crown of a facetted gemstone.

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

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

Tone
The relative lightness or darkness of a color.

Translucent
A substance that allows transmitted light to clearly pass through. Objects cannot be seen through a translucent substance.

Transparent
A substance that allows transmitted light to clearly pass through. Objects can be seen through a transparent substance.

Trichroism
The transmission of three different colors in three different optical planes as light passes through a gemstone material. May be used to distinguish one gemstone material from others.

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

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

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

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

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

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

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