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GIA Diamonds
Vocabulary for GIA Diamond Course
| Term | Definition |
|---|---|
| Abrasion (Abr) | A series of minute nicks along the facet junctions of a fashioned diamond; gives the edges a white or fuzzy appearance. |
| Adamantine luster | The highest degree of luster possible in a transparent material. |
| Aggregate | A solid mass of individual, randomly oriented crystals, intergrown or held together by a natural binding agent. |
| Alluvial deposit | A deposit where gems are eroded from their source rock, then transported away from the source and further concentrated. |
| Angle of incidence | The angle at which a ray of light strikes a surface, measured from the normal. |
| Angle of reflection | The angle between the normal and a reflected ray of light. |
| Annealing | Using heat to stabilize irradiated color in gemstones. |
| Appraisal | An estimation of the value of an article, usually for insurance purposes. |
| Average girdle diameter | The result achieved by adding the smallest and largest girdle measurements of a round brilliant and dividing by two. |
| Bast | Frosted rough diamond. "Bark" in Dutch. |
| Bearded Girdle (BG) | Very small feathers that extend from the girdle surface into the stone; can result from the cutting process. |
| Belly | The slightly curving center of the long side of a pear, marquise, heart, or oval. |
| Beneficiation | A commitment to reserve a portion of the resources derived from any country for the economic development of that country. |
| Best Practices Principles (BPP) | De Beers' formalized commitment of itself and its sightholders to the highest ethical standards. |
| Blemish | Clarity characteristic that's confined to the surface of a polished gemstone. |
| Block caving | Underground mining that involves building a concrete-lined tunnel under an ore deposit, then collecting the ore through openings in the liner. |
| Blocking | Placing the first 17 or 18 facets on a diamond. |
| Bow-tie | A dark area across the center of an elongated brilliant cut. |
| Brick-and-mortar retailer | A traditional store consisting of walls and a fixed location. |
| Brightness | The effect of all the diamond's internal and external reflections of white light. |
| Brilliant cut | A cutting style in which triangular and kite-shaped facets radiate from a gem's center toward its girdle. |
| Brillianteering | Placement and polishing of the star and upper and lower girdle facets. |
| Bruise (Br) | A tiny area of impact accompanied by very small, root-like feathers visible at 10X magnification; typically occurs at a facet junction. |
| Bruting | Forming the basic face-up outline of a diamond to prepare it for faceting. |
| Bulk sampling | Large-scale character sampling. |
| Burn Marks (Brn) | Hazy surface areas that result from excessive heat or from uneven polishing caused by structural irregularities; also called polish marks or burned facets. |
| Cavity (Cv) | An angular opening created when part of a feather breaks away. |
| Central Selling Organisation (CSO) | An agency designed to purchase, sort, evaluate, and sell rough diamonds. |
| Character sampling | Testing for the size, shape, clarity, and color of the diamonds in a deposit. |
| Characteristic color | The basic color of a fancy-colored diamond. |
| Chemical vapor deposition (CVD) | An industrial process adapted to allow growth of synthetic diamond from carbon-rich gas in thin layers onto a silicon or diamond surface. |
| Chip (Ch) | A shallow opening caused by damage to the stone's surface; typically occurs at a girdle edge, facet junction, or culet. |
| Clarity characteristic | Internal or external feature of a gemstone that helps determine its quality and establish its identity. |
| Cleavage (Cl) | Large, severe, straight break along a plane of atomic weakness; considered an inclusion. |
| Cleavage plane | Plane parallel to a possible crystal face, where a diamond can split cleanly when struck. |
| Cleaver | A person who cleaves, or splits, a diamond along a cleavage plane. The cleaver might also be responsible for planning the fashioning of a polished gem. |
| Cleaving | Dividing a diamond into two or more pieces along a cleavage plane. |
| Cloud (Cld) | Many tightly grouped pinpoints that might be too small to distinguish individually at 10X but together have a hazy appearance. |
| Color center | Structural defect that influences an object's absorption of light and can cause its color. |
| Conflict diamonds | Diamonds used to finance violence and terror. |
| Consignment | A selection of goods loaned to a dealer by another wholesaler or manufacturer. |
| Core | Earth's innermost layer. |
| Covalent bond | A chemical bond formed by two atoms sharing electrons. |
| Craftsmanship | The care that goes into the fashioning of a polished diamond, as confirmed by its finish. |
| Cratons | Ancient, large, and stable parts of the earth's continental crust. |
| Critical angle | Angle between the normal and the maximum angle of refraction, which is the largest angle at which rays inside the diamond can escape. |
| Cross worker | A person who performs the cross-working operations during diamond polishing; sometimes called a cross cutter. |
| Cross working | Placing the bezel and pavilion facets on round and fancy shapes. Sometimes combined with blocking, especially on smaller stones. Also called cross cutting. |
| Crown angle | The angle formed by the bezel facets and the girdle plane. |
| Crown height percentage | The distance from the girdle plane to the table, expressed as a percentage of average girdle diameter. |
| Crust | The surface and outermost layer of the earth. |
| Crystal | Solid matter with atoms arranged in a regular, repeating pattern. |
| Crystal (Xtl) | A mineral crystal contained in a diamond. |
| Crystal planes | Internal directions parallel to a mineral's unit cell surfaces. |
| Crystal shape (form) | Geometric shape of a well-formed crystal. |
| Crystal structure (lattice) | Regular, repeating arrangement of atoms in a mineral. |
| Crystal systems | Categories of crystals based on their symmetry and internal structure. |
| Crystalline | Composed of crystals or related to crystals. |
| Culet size | The size of the facet at the bottom of the diamond where the pavilion mains meet. |
| Cuttable rough | Diamond rough with good enough size, shape, clarity, and color to produce a polished stone suitable for use in jewelry. |
| Cutting center | A city, region, or country with a large number of gemstone manufacturers. |
| Cutting style | The arrangement of a gem's facets. |
| Electronic retailer | Business that sells to consumers via television cable, phone line, or satellite. |
| Emplacement | A geologic process that delivers materials (sometimes diamonds) to the surface. |
| Etch Channels | Angular openings that start at the surface of the diamond and extend into it, often with striations perpendicular to their length; considered inclusions. |
| Extra Facet (EF) | A small facet that's not required by the cutting style, placed without regard for the diamond's symmetry; most often found near the girdle. |
| Eye-visible | Visible to the unaided eye, without magnification. |
| Face-down (or table-down) | A position that orients a gemstone's pavilion toward the viewer. |
| Face-up | A position that orients a gemstone's crown facets and table toward the viewer. |
| Face-up (or table-up) | A position that orients a gemstone's crown toward the viewer. |
| Fancy cut | Any gemstone shape other than round. |
| Fancy-colored diamonds | Diamonds that exhibit yellow or brown color beyond the Z range, or that exhibit any other color. |
| Feather | A trade term for any break in a diamond. |
| Feather (Ftr) | General trade term for a break in a gemstone. Often white and feathery in appearance. |
| Finish | The quality of the polish and precision of the cut of a fashioned gemstone. |
| Fire | The flashes of color you see in a polished diamond. |
| Flash effect | A flash of changing color seen in a fracture-filled diamond when you look parallel to the filled inclusion and rock the diamond back and forth under magnification. |
| Fluorescence | Emission of visible light by a material when it's exposed to ultraviolet radiation. |
| Foilback | Gemstone or simulant with a thin metallic foil or mirroring film applied to its pavilion. |
| Foss | Irregular furrow or groove in the surface of a diamond, characteristic of diamond crystals in the gray color range. |
| Four-point diamond | A diamond with the table parallel to a possible cubic face. |
| Fracture filling | Treatment that involves injecting a molten glass substance into a diamond's surface-reaching feathers or laser drill-holes. |
| French tips | A faceting style that replaces the large bezel facets at the points of marquises, pears, and hearts with star and upper girdle facets. |
| Girdle thickness | The width of a fashioned gem's girdle. |
| Girdle thickness percentage | Girdle thickness expressed as a percentage of average girdle diameter. |
| Glassie | A well-shaped, transparent, octahedral diamond crystal with sharp, square edges. |
| Gletz | Dutch term for a feather in a diamond. |
| Glide plane | Crystal distortion caused during growth when one part of the lattice is offset in relation to the rest. |
| Grade-setting characteristics | Inclusions or blemishes that establish the clarity grade of a diamond. |
| Grain Center (GrCnt) | A small, concentrated area of crystal distortion; can be white or dark, and might appear thread-like or pinpoint-like. |
| Graining (grain lines) | Visible, shadow-like lines in a diamond caused by irregularities in the crystal structure. |
| Graphitization | Graphite formation around a diamond's mineral inclusions and feathers that results from the extreme conditions of HPHT processing. |
| Gravity sorting | Separating heavier materials (diamonds) from a test sample. |
| Grease belt | An apparatus that uses diamonds' affinity for grease to separate them from other minerals. |
| Habit | Characteristic crystal shape of a specific mineral. |
| Half-life | The length of time required for half of a group of atoms of a particular type (radioactive) to decay into another type (non-radioactive). |
| High pressure, high temperature (HPHT) | Diamond synthesis method that mimics the pressure and temperature conditions that lead to natural diamond formation. |
| Igneous | A category of rocks formed from a molten state. |
| Improvables | Diamonds that can be repolished to improve their clarity to a VVS1 or VVS2 grade. |
| Inclusion | Clarity characteristic totally enclosed in a polished gemstone or extending into it from the surface. |
| Indented Natural (IndN) | A portion of the rough's original surface, or skin, that dips below the polished diamond's surface, or an opening left when a surface-reaching crystal drops out or is forced out during polishing. |
| Indicator minerals | Minerals formed together with diamonds at great depths and brought to the surface by the same kimberlites or lamproites. |
| Industrial rough | Diamond rough suitable for use in tools, drills, abrasives, and other industrial applications. |
| Internal Graining (IntGr) | Lines, angles, or curves that might appear whitish, colored, or reflective or affect transparency at 10X; caused by irregularities in crystal growth. |
| Internal laser drilling (ILD) | A clarity treatment that uses a laser to expand an existing cleavage or create a new one, allowing the introduction of a bleaching solution. |
| Irradiation | Exposure of a material to radiation; causes color change in diamonds. |
| Kaps | Dutch term for a diamond that has been cleaved, split, or sawn, but not fashioned. |
| Kerf | A notch scratched into diamond rough to prepare it for cleaving. |
| Kimberley Process (KP) | Diamond industry program designed to ensure that diamonds crossing international borders are legitimate and do not fund civil conflict or terrorism. |
| Kimberlite | An igneous rock that transports diamonds to the surface. |
| Knot (K) | An included diamond crystal that extends to the surface after fashioning. |
| Lamproite | An igneous rock, rarer than kimberlite, that transports diamonds to the surface. |
| Laser Drill-hole (LDH) | A tiny, surface-reaching tunnel produced by a laser light beam. |
| Laser drilling | Using a concentrated beam of laser light to reach a diamond's dark inclusions and disguise or eliminate them. |
| Laser Manufacturing Remnants (LMR) | Internal fractures (inclusions) or surface grooves (blemishes) created as a result of laser marking or manufacturing. |
| Length-to-width ratio | A numerical expression of the relationship between the length and width of a fancy cut, where the value for width is one. |
| Linear accelerator | A machine used to accelerate electrons to high energy along a straight path. |
| Lizard Skin | Wavy or bumpy area on the surface of a polished diamond. |
| London Diamond Syndicate | A group of diamond merchants that united in 1890 to buy and sell rough diamonds. |
| Lot price | A discounted price for buying an entire parcel, or a substantial part of it. |
| Lower girdle facet percentage | The length of the lower girdle facets expressed as a percentage of the total distance between the girdle and the culet. |
| Luster | The appearance of a material's surface in reflected light. |
| Macle | A flat, triangular twinned diamond crystal. |
| Mantle | Layer between the earth's crust and its core. |
| Marine deposit | Secondary diamond deposit carried by rivers or streams to the ocean floor or shoreline. |
| Master-eye effect | The optical illusion that causes the ungraded diamond to appear either lighter or darker than the masterstone, depending on which side it's on. |
| Masterstones | A set of color-comparison diamonds that defines GIA diamond color grades in the normal (D-to-Z) range. |
| Matching tray | A grooved, white, non-reflective tray used for matching sets of stones. |
| Memo | Buying agreement where a dealer entrusts merchandise to a customer for inspection and approval without requiring immediate payment. |
| Microdiamond testing | Screening for the presence of tiny diamonds in a sample. |
| Mixed cut | A cutting style that combines step-cut and brilliant-cut facets. |
| Naif | The natural, unpolished surface of a rough diamond. |
| Natural (N) | A portion of the original surface, or skin, of a rough diamond left on a fashioned stone; usually on or near the girdle. |
| Natural Radiation Stain | Green or brown patch of color, usually seen around the girdle on the surface of a cut diamond. Typically a blemish, but can be an inclusion if it extends into the stone. |
| Near-gem | Diamond rough whose color and clarity is such that it can be either polished or used industrially, depending on market conditions. |
| Needle (Ndl) | A long, thin crystal that looks like a tiny rod at 10X. |
| Nick (Nk) | A small notch on a facet junction with no readily apparent depth at 10X, usually along the girdle edge or at the culet. |
| Normal | An imaginary line perpendicular to the point where a ray of light strikes the surface. |
| Normal color range | Range of diamond colors from colorless to light yellow and light brown, also called the D-to-Z range. |
| Octahedron | A form with eight equal triangular sides. |
| Old European cut | An early brilliant cut with a circular girdle. |
| Old-mine cut | An early cushion-shaped brilliant with a high crown, deep pavilion, and 58 facets including a large culet. |
| Open-pit mining | Removal of mineral-bearing ore from a large surface excavation. |
| Ore grade | Concentration of diamond in a potentially mineable deposit. |
| Overburden | Sand, gravel, or rock that covers a diamond pipe. Must be removed to reach diamond-bearing ore. |
| Painting | A weight-retention method that adjusts the angles of some facets to allow portions of a diamond's girdle to be thicker. |
| Parcel | A quantity of stones, sometimes of similar size and quality, packaged together for sale or storage. |
| Pattern | The relative size, arrangement, and contrast of bright and dark areas that result from a diamond's internal and external reflections. |
| Pavilion angle | The angle formed by the pavilion mains and the girdle plane. |
| Pavilion bulge | Outward curve of the pavilion facets of a step-cut diamond. |
| Pavilion depth percentage | The distance from the girdle plane to the culet, expressed as a percentage of average girdle diameter. |
| Per-carat price | The price of a gem divided by its carat weight. |
| Pick price | A premium price for selecting stones from a parcel. |
| Pinpoint (Pp) | A very small included crystal that looks like a tiny dot at 10X. |
| Pipe | A deep vertical formation at the earth's surface that results from a kimberlite or lamproite emplacement. |
| Pit (Pit) | A small opening that looks like a tiny white dot. |
| Planner | The person who decides where to mark diamond rough for fashioning into the most profitable polished gem. |
| Plot | A map of a diamond's inclusions, blemishes, and facet arrangement. |
| Point naif | A seventeenth-century term for a diamond octahedron or other crystal shape on which the natural faces are apparent. |
| Polish | The overall condition of the facet surfaces of a finished diamond. |
| Polish Lines (PL) | Fine, parallel grooves and ridges left by polishing; can occur on any facet but do not cross facet junctions; transparent or white. |
| Polishing | Placing and finishing facets on a rough diamond. Also called faceting. |
| Potentials | Diamonds that can be repolished to improve their clarity to an Internally Flawless grade. |
| Primary crushing | Reduction of newly mined ore to a manageable size. |
| Primary deposit | Gems found in the rock that carried them to the surface. |
| Proportions | The angles and relative measurements of a polished gem and the relationships between them. |
| Recovery | Any method used to separate diamonds from ore or alluvial sediments. |
| Recutting | Repairing damage or refashioning a polished diamond to improve its clarity, proportions, or color, or to modernize an old-style cut. |
| Reflection | The bouncing back of light when it strikes a surface. |
| Refraction | Change in speed and possible change in direction of light as it travels from one material to another. |
| Refractive index (RI) | A measure of the change in the speed and angle of light as it passes from one material to another. |
| Relief | Contrast between an inclusion and its host gem. |
| Repolishing | Refinishing a polished diamond to correct minor faults in its clarity or finish. |
| Rhinestone | A foilbacked, colorless, lead-glass diamond imitation. |
| Rough Girdle (RG) | Irregular, pitted, or granular girdle surface. |
| Sawing | Dividing diamond rough into sections, either mechanically or by laser. |
| Scaife | A rapidly spinning horizontal disc coated with diamond powder, used to polish diamond rough. |
| Scintillation | The flashes of light and the contrasting dark areas you see when the diamond, the light, or the observer moves. |
| Scoop | A small shovel made of thin metal, used for picking up gems. |
| Scratch (S) | A thin, dull white line across the diamond's surface; shows no apparent depth at 10X. |
| Scrubber | An apparatus that washes away dirt and clay from diamond-bearing ore. |
| Secondary deposit | Gems found away from their primary source. |
| Selective absorption | Process by which a material absorbs some wavelengths of light and transmits others. |
| Separation | Process of distinguishing natural minerals and gems from each other as well as from synthetics, simulants, and treated gems. |
| Shape | The face-up outline of a gem. |
| Shape appeal | A diamond's overall attractiveness in relation to others of the same shape and cutting style. |
| Sharp | A small diamond with a sharp edge, cemented into a dop and used to kerf another diamond in preparation for cleaving. Or, a small diamond used to brute diamonds or round up a girdle in the final stages of polishing. |
| Sieve set | Set of circular plates, each punched with precisely sized holes, used for sorting small, round gems by size. |
| Sight | Trading event where selected clients buy rough diamonds. |
| Sightholder | A diamond manufacturer or dealer invited by De Beers to buy rough diamonds. |
| Single cut | A simple diamond cut, with a table, eight crown facets, eight pavilion facets, and sometimes a culet. |
| Single-channel marketing | A direct, centrally controlled marketing route for rough diamonds. |
| Singly refractive (isotropic) | Possessing the same physical or optical properties in all crystal directions. |
| Sorting pad | A pad of white paper for sorting and showing gems. |
| Sparkle | The spots of light that flash as the diamond, the observer, or the light source moves. |
| Special | A rough diamond over 10.80 cts., sold separately to a sightholder who specializes in larger stones. |
| Specific gravity (SG) | Ratio of the weight of a material to that of an equal volume of water. |
| Splitter | A person who splits a rough diamond along a cleavage plane after it has been kerfed by a laser. Not to be confused with a cleaver, who is a master craftsman. |
| Star facet length percentage | The length of the star facets expressed as a percentage of the total distance between the girdle and the edge of the table facet. |
| Step cut | A cutting style with long, narrow, four-sided facets in rows parallel to the girdle on both the crown and pavilion. |
| Subduction | Process in which two crustal plates collide, forcing one under the other. |
| Supplier of Choice | Program adopted by De Beers in 2001, in which it required its sightholders to help increase market demand for diamonds. |
| Supplier of Choice 2 | Program adopted by De Beers in 2007 to answer critics and resolve shortcomings of its original SOC program. |
| Surface Graining (SGr) | Similar to internal graining, except it appears on the surface; results from irregularities in the crystal structure. |
| Symmetry | The exactness of a finished gem's shape and the placement of its facets. |
| Synthetic diamond | Manufactured diamond with essentially the same physical, chemical, and optical properties as natural diamond. |
| Table gauge | A transparent measuring device divided into millimeters and tenths of a millimeter, used to measure a diamond's table. |
| Table percentage | A diamond's table size expressed as a percentage of its average girdle diameter. |
| Tang | A device that holds the dop and allows polishers to adjust and maintain a diamond's angle during polishing. |
| Tetrahedron | In diamond, a group of five carbon atoms with one at the center. |
| Thermal conductivity | The relative ability of a material to transfer heat. |
| Thermal expansion | Capacity of a material to expand when it's heated. |
| Thermal tester | An instrument that measures thermal conductivity to help separate natural and synthetic diamonds from most simulants. |
| Three-point diamond | A diamond with its table nearly parallel to a possible octahedral face. |
| Total depth percentage | Table-to-culet depth, expressed as a percentage of average girdle diameter. |
| Trace elements | Atoms in a gem that aren't part of its essential chemical composition. |
| Transmission | The passage of light into or through a material. |
| Twinned crystal | Crystal distorted during growth, with two or more intergrown crystals with opposing crystal directions. |
| Twinning Wisp (W) | A series of pinpoints, clouds, or crystals that forms in a diamond's growth plane; associated with crystal distortion and twinning planes. |
| Twisted stone | A diamond with grain layers that are not on parallel planes, or one with partial twinning. |
| Twisting | A blocking technique in which the diamond is turned to position the softest polishing direction against the polishing wheel. |
| Two-point diamond | A diamond on which the table has been polished parallel to a dodecahedral plane. |
| Unit cell | Smallest group of atoms with the characteristic chemical composition and the basic crystal structure of a mineral. |
| Vertical integration | Involvement of a business or industry in all aspects of its product's market. |
| Water | A historic term once used in Europe to describe either the color or the transparency of a diamond. |
| Wavelength | The distance between two adjacent high points of an energy wave. |
| Wholesaler | Someone who sells to retailers rather than directly to consumers. |
| X-ray separation | A recovery method that uses X-rays to detect diamonds and an air jet to remove them from ore. |
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ahylton2517