Glossary

Vocabulary
Abraded culet	When the small culet facet becomes chipped or scratched by another diamond, or resulting from being carried loose in a diamond paper with other diamonds.
Adamantine	Diamond like. The appearance of a material's surface in reflected light, as determined by the quantity and quality of light reflected. The luster of most cut and polished diamonds is described as adamantine luster.
Alluvial deposits	Sometimes environmental forces break down the kimberlite at the surface of the pipe, and diamonds get washed out of the pipe into riverbeds. These riverbeds (or ancient riverbeds) are referred to as alluvial or secondary deposits.
Amsterdam	In Holland , a traditional diamond cutting center that has declined markedly in recent years, although it was very important at one time.
Antwerp	In Belgium , the most important diamond cutting center in the world and a major distribution center for polished goods.
Bahia	A gem producing state in Brazil , diamonds were discovered here as early as 1755. Bahia is also an important source of carbonado.
Bezel facets	The eight large, four sided facets on the crown of a round, brilliant-cut diamond, the upper points of which join the table and the lower points, the girdle.
Black diamond	When a diamond is dark gray, a very dark hue, or truly black, it is referred to in the trade as a black diamond. Such a stone may be opaque to nearly semi-transparent.
Blemishes	Imperfections in a diamond that are confined to the surface of the stone.
Blocking	The process of placing the first 18 (main) facets on a diamond brilliant (17, if there is no culet) while fashioning a diamond.
Boron	One of the many impurities in diamond which is now believed to cause the semi-conductor properties and the blue color in Type IIb diamonds.
Bort (also Boart)	The lowest quality of diamond so badly flawed and imperfectly crystallized that it is suitable only for crushing into abrasive powders for a multitude of industrial purposes.
Brilliance	Brilliance is the quality and quantity of light returned from reflections within the gemstone to the eye.
Brillianteering	The placing and polishing of the 40 remaining facets on a brilliant-cut diamond after the main bezel and pavilion facets have been placed and polished by the blocker.
Bruting	The step in the fashioning process of a diamond in which the stone is given its circular shape.
Canary diamond	A trade name for an intensely colored yellow diamond. The yellow may be very slightly greenish or slightly orangy, but it must be deep enough to be an asset. Such a diamond is called a fancy.
Cape	A broad range of diamond color grades for stones that show a distinct yellow tint face-up.
Cape spectrum	Diamonds with a significant depth of yellow body color of natural origin frequently show a characteristic absorption spectrum when examined with the spectroscope. Since yellow stones are known as capes, the absorption lines are often called Cape lines of Cape spectrum.
Carat	A unit of weight for diamonds and other gems.
Carbon	A non metallic chemical element C, occurring native in the crystalline form as diamond, graphite and lonsdalite.
Carbonado	Black industrial diamond, a massive, impure, slightly cellular aggregate of minute diamond crystals, forming a mass with a granular to compact structure. It is the toughest form of industrial diamond.
Carob seeds	The origin of the 'carat weight' stems from the seed of carob tree. The dried dark-colored seeds are very uniform in weight and were first used by ancient pearl merchants as units of weight.
Central Selling Organization (CSO)	De Beers created the Central Selling Organization (CSO) to market their rough diamond production through their office in London , to ensure that the world's diamond markets receive the rough diamond required to meet their needs.
Certificate	A written report describing a diamond as to its weight, proportions, color grade and clarity grade.
CIBJO	Acronym for the French equivalent of the International confederation of Jewelry, Silverware, Diamonds, Pearls and Stones. CIBJO is a European organization which has established rules of nomenclature and their application for gem materials.
Clarity	Clarity refers to a diamond's purity.
Cleavage	Cleavage refers to the tendency of a single crystal to break or split along smooth flat planes parallel to atomic planes.
Cleaving	A process occasionally used in fashioning diamonds. The splitting of a stone along a cleavage plane, or grain, into two or more portions, to produce pieces of a size or shape that will produce fashioned stones more economically or of better qualities.
Color center	A structural defect in the atomic lattice of a mineral that absorbs light.
Color grade	The relative position of a diamond's body color on a colorless-to-yellow scale.
Crown	That portion of any faceted gemstone above the girdle.
Crown angle	The angle measured between the table and the crown facets and is read as the reciprocal angle.
Crown height	The distance from the girdle to the table.
Crown height	The vertical distance between the girdle plane and the table.
Crystalline	Gems with orderly atomic structures are termed crystalline.
Crystal	The term crystal refers to a crystalline substance that displays outward signs of its internal symmetry - it shows flat surfaces ('faces').
Crystal form	The geometric form or shape of a crystal, e.g., a common diamond form is an octahedron.
Cutting shapes	Shape refers to the basic girdle outline of a stone.
De Beers Consolidated Mines, Ltd	Privately owned company formed in 1888 in South Africa, controlling the major production and distribution of rough diamonds.
Depth percentage	The depth percentage is calculated by measuring the depth of the diamond (the distance from the table to the culet) in millimetres, and dividing that number by the average girdle diameter, which is also measured in millimetres.
Diamond Trading Company (DTC)	DTC is the marketing arm of the De Beers group of companies. DTC sorts, values and sells the majority of the world’s rough diamonds.
Diamond appraisal	A monetary evaluation of a diamond or diamond jewelry, usually for insurance or estate purposes. An appraisal is only an opinion on the identity, quality, and value of a diamond at a given point in time.
Diamond Bourse	A wholesale diamond exchange dealing mainly in polished stones. The Diamond Exchange with the purpose of protecting trade’s integrity and interests with its own infrastructure, constitution and by-laws and strict requirements for membership.
Diamond sieve	A round, perforated metal plate for rapid grading of loose, fashioned diamonds for size. A number of such plates are usually used, each having perforations of a different size.
Dispersion	Dispersion is the breaking up of white light into its six component colors of red, orange, yellow, green, blue, and violet.
Dop	Any device that is used to hold a diamond during the sawing or faceting process. A cutter's dop is usually made of bronze or copper with either a cup-like or flat surface to which the diamond is fixed with "cutter's cement".
Doublet	A composite assembled stone usually of two parts, crown and pavilion, cemented or fused together. Diamond doublet has a diamond top and pavilion of synthetic colorless sapphire or spinel, quartz, glass etc.
Durability	Durability depends on a combination of many factors, particularly hardness and toughness.
Electric conductivity (of diamond)	The electrical resistance of diamond is very high: therefore, it is essentially a non conductor.
Extinction	Should the pavilion be too deep, light passes out the side and extinction results, also referred to as black center.
Eye clean	A term that implies that no internal flaws are visible to the unaided eye of a qualified diamond clarity-grader.
Fancy colored diamonds	All other natural colors in diamond are considered fancies regardless of hue and tone.
Four C’s	Color. Clarity, Cut and Carat weight.
Gemstone fashioning	The cutting and polishing of a gemstone from the rough to a finished stone.
Girdle diameter	External circular diameter of a diamond. Girdle separates the crown to the pavilion of a diamond.
Grain	The atoms of a diamond are arranged in planes. This is termed the "grain" of the diamond, and is similar to the grain in a piece of wood.
Grainer	Stones with weights near multiples of 0.25 cts, or one grain, are referred to as grainers, qualified by the appropriate numerical designation, e.g.: four-grainer for a one-carat stone.
Hardness	Hardness is the resistance to scratching of a smooth surface.
HPHT	High pressure - high temperature. A treatment process developed to improve color in a diamond using high pressure high temperature technique.
Hue	The pure color defined by position on the color spectrum; what is generally meant by ‘color’ in lay terms.
Ideal cut	The term ideal cut, used predominantly for round brilliant stones refer to the set of proportions that yield the highest degree of brilliance. These were calculated by Marcel Tolkowsky who published his findings in 1919. The objective in faceting a gemstone is to achieve beauty through brilliance, scintillation and dispersion. A faceted stone is designed to be a light trap - to collect as much light as possible - and throw it back to our eyes.
Inclusion	Any visible internal foreign object, or any crystal or grain of the same material as the host, or any break in a diamond or other gemstone can be called an inclusion.
Inclusions	Imperfections in a diamond that are found inside the stone.
Inert	No detectable reaction, such as fluorescence, to stimulus when exposed to radiation from x-rays, ultraviolet or cathode rays.
Kimberlite	The Kimberly Process ensures that conflict or illicit unofficial rough diamonds will be excluded from the legitimate distribution channels.
Loupe	Any small magnifying glass mounted for use in the hand as a hand loupe. A loupe usually contains a system of lenses (corrected) to the minimum specifications for a magnification of 10x power.
Macle	A term used in the diamond trade for a flat, triangular rough diamond, which is a twinned crystal.
Make	A trade term that refers to the proportions and finish of a diamond; for example, good make refers to a stone that is well proportioned, symmetrical and well polished.
Master diamonds	Fashioned diamonds of known color grades that are used as comparison stones when grading other diamonds for body color.
Melee	From the French, meaning a confused mass, a skirmish, an affray, etc. 1) In the trade, the term is used collectively to describe smaller brilliant-cut diamonds. 2) Usually, all small gemstones used in embellishing mountings, settings, or larger gems are called melee.
Microscope	An optical instrument that affords visual magnification of objects. A binocular microscope is equipped with twin objectives and occular and provides normal three-dimensional viewing.
Mumbai (Bombay)	A major diamond cutting and marketing center in India .
Nitrogen	Non-metallic, colorless element symbol N, and a diatomic gas (N2). Occurs as a trace element inclusion in the lattice in some diamonds. Nitrogen occurs as aggregate in Type Ia or as dispersed-atoms in Type II diamonds. The presence of nitrogen dispersed through the crystal lattice in the order of one part in a million is believed to cause the diamond to absorb light in the blue region which results in the yellowish-body color of Type I diamonds.
Pavilion	That portion of a faceted diamond or other gemstone below the girdle. Also known as base.
Pavilion angle	The angle between the girdle plane and the pavilion main facets.
Pavilion depth	The distance from the girdle to the culet.
Pavilion facets	Those facets on any fashioned stone located on the pavilion, or base (i.e. below the girdle), as opposed to the crown facets, which are located above the girdle.
Polymorph	Special word for different minerals that have exactly the same chemical composition.
Polymorphism	The ability of an element of particular compound to crystallize in more than one pattern or crystal structure is called polymorphism.
Primary deposits	Diamonds are mined directly from the rock in which they were brought to the surface.
Rapaport Diamond Report	A weekly New York publication, which gives so-called "spot cash" asking prices for well-cut diamonds of specific color, clarity and carat weight.
Refractive index (R.I)	Refractive index (RI) is expressed as a ratio of the speed of light in air to the speed of light in a substance.
Round brilliant	The brilliant cut is aimed at providing a combination of brilliance, "fire" (dispersion) and scintillation ("sparkle").
Round brilliant cut	The standard round brilliant cut consist of either 57 (no culet) or 58 (with culet) facets. The most common style of cutting for diamonds.
Saturation	The purity of color, going from the lightest tint to the deepest, most saturated tone.
Sawing	The phase of the diamond-fashioning process in which a crystal is separated by abrading or grinding a narrow slit through it. The sawing operation is performed by holding the diamond against a rapidly revolving disc. The stone is carefully mounted in a dop and placed in a weighted arm, to hold it against the saw.
Scintillation	Sparkle in a gemstone is termed scintillation, the twinkling of a faceted gem when either the eye the light or the stone itself is moved.
Selective absorption	The stone's ability to absorb certain wavelengths of white light while transmitting the remaining portions.
Single cut	Also called 8-cut. Extremely simplified form of the brilliant cut used for small diamonds usually below about 2mm. Diameter. Usually has 17 facets (no culet); 8 facets surround the table facet and 8 facets on the pavilion.
Single refraction (SR)	The inability of a gemstone to polarize light passing through it, thus permits the light to pass through as a singly refracted beam. Diamonds and other minerals of the cubic, or isometric, crystal system are isotropic.
Solitaire	A term used to refer to a ring containing a single diamond or other gem.
Sorting	General term for separating rough crystals or cut and polished diamonds into groups of similar characteristics including size, shape, quality and color.
Specific Gravity (S.G)	Specific gravily is a ratio comparing the weight of a material (in air) to the weight of an equal volume of water at 4°C.
Spectroscope	An optical instrument for determining the absorption spectrum of a transparent material.
Surface Luster	The surface luster or, simply, luster of a gemstone is the quality and quantity of light that is reflected from the surface of the gemstone back to the eye.
Synthetic diamond	A man-made diamond produced artificially by subjecting a carbonaceous material to extremely high temperature and pressure.
Table	The largest facet that caps the crown of a faceted diamond of other gemstone. In the standard round-brilliant, it is octagonal in shape and is bounded by eight star facets.
Table size	1) The size of the table of a faceted diamond, expressed as a percentage of the stone's diameter, is a dimension used in proportion analysis. 2) Table size is measured under microscope in at least two directions, the distance between two opposite 'corners' of the table.
Tang	A special clamp or tool holder in which the dop holding a diamond is held for polishing.
Tavernier ,Jean Baptiste (1605 - 1689)	A famous French gem dealer and traveler who made six journeys to the East, where he inspected the treasures of the many potentates and rulers of that time. He described his experiences in a book called 'Les Six Voyages de Jean Baptiste Tavernier', a work to which the world owes the descriptions of many of the famous diamonds and other gems of the world, both actual and legendary.
The Guide	Published quarterly in the U.S.A. , it is used as a general price reference by many American retailers.
Thermal Inertia (Thermal conductivity)	Thermal inertia or thermal conductivity is a measure of how quickly heat passes through a material. Type IIa diamonds are far better thermal conductors than Ia or Ib diamonds.
Tolkowsky, Marcel	A mathematician who worked out and published the proper proportions for maximum brilliancy consistent with a high degree of fire, or dispersion, from a round brilliant. (Diamond design, London, 1919). His results came to be called the American cut or Ideal cut.
Tone	Refers to the relative lightness or darkness of a color.
Total depth	The distance from the table to the culet.
Toughness	Toughness refers to the ease with which a break of any kind can be produced in the stone.
Transparency	Transparency is the ability of a material to transmit light without distortion.
Trigon	A triangular marking, either an indentation or a raised equilateral triangle, occurring as a growth mark on diamond octahedron faces.
Type classification (Diamond)	Diamonds could be divided into two major categories, Type I and Type II diamonds, according to their transparency to ultraviolet light, infrared absorption spectra and other physical properties.
Ultraviolet lamp	A source of ultraviolet radiation used for exciting fluorescence in diamonds and other gems.
Window	If the pavilion is too shallow, light leaks out through the bottom and a window results, also referred to as fish-eye.