Abrasion A bruise or scratch on a fashioned diamond.
Adamantine Lustre A very bright and reflective lustre typically displayed by diamond. From the Greek word ‘adamas’ meaning unconquerable or indestructible (See ‘lustre’).
Alluvial deposit Deposits of minerals formed by the action of water eroding and transporting rock material (See ‘Gem Gravels’).
Anisotropic Crystal which exhibits double refraction (D.R.) The crystal breaks up a ray of light into two rays which move with different velocities within the crystal (See ‘Double Refraction’).

Baguette A rectangular shaped step cut.
Bearding Minute, hair like feathers extending into a polished stone from the girdle caused in the fashioning process.
Blemish A surface imperfection on a fashioned diamond e.g. nick, scratch, abrasion.
Brilliance The return of light through the crown facets and surface of a gem, resulting from light reflecting from the pavilion facets.
Brilliant Cut Collective name for diamond cuts whose lower facets radiate from the centre of the stone towards the girdle, the most common of which is the round cut.
Bruting The process of shaping the rough stone into its eventual polished shape along the girdle.
Burn Mark A frosted surface effect on a stone due to overheating during the polishing stage or when the diamond is mounted and being repaired.

Cape (Colour) Old term used to describe diamonds with a distinct yellow tint.
Carat Standard weight unit for gemstones; 1 carat = 0.20 grams.
Certificate Document provided by an accredited laboratory, such as AnchorCert, stipulating the stone’s weight, colour, clarity, cut and proportions.
Clarity A stone’s relative freedom from inclusions and imperfections. Expressed in a fixed grading scale.
Clarity Characteristics Inclusions can become part of a diamond during formation or result from the crystal structure. They might also result from damage to the stone or be introduced during cutting or treatment. They affect the diamond’s clarity grade when viewed through 10X magnification.
Cleavage A flat break or fracture in the stone which may be internal or surface reaching. These usually occur along the crystal’s growth planes (see also ‘Feather’).
Cloud A group of tiny inclusions to give a clouded appearance.
Coating When a gemstone is coated on the pavilion, girdle or entirely to improve or change the overall colour of the stone.
Colour A general term used to describe a basic factor that affects a diamond’s beauty and value. Colours range from colourless to yellow or brown. (See ‘Fancy Colour’)
Crown The part of the stone located above the girdle.
Crystal Inclusion An impurity within a stone with a geometric, crystal-like shape.
Culet  The small facet at the point of the pavilion.
Cubic Zirconia (C.Z.) Manmade gem. Zirconium Oxide stabilised in the cubic system. The most common diamond imitation.
Cut  The cut refers to the diamond’s overall shape. It also refers to the proportions and finish to the polished diamond.
C.V.D. Diamond A synthetic diamond produced by a process of chemical vapour deposition.

Diamond A carbon based mineral created under extreme pressure and temperature. Diamond is the hardest of all known substances and exists in a variety of colours ranging from white to fancy colours.
Dispersion The splitting of white light into the spectral colours observed as spectral flashes of colour at the surface of a well faceted diamond and some other stones. (See ‘Fire’)
Double Refraction The optical doubling effect caused by the splitting of visible light into two separate components by an optically anisotropic material. (See ‘Anisotropic’)
Doublet A composite gemstone consisting of two parts of the same or different materials joined together.
Durability A combination of hardness, toughness and stability within a gemstone.

Emerald Cut Rectangular or square step cut with diagonally cut corners.
Enhancement Artificial alteration of the appearance and properties of gem material, in order to improve its appearance, stability and sale ability.
Extra facet Any facet added to the stone which is in excess of the facets normally required to complete the polishing. Usually found along the girdle to remove any imperfections.

Facet Flat polished surface on a polished stone.
Fancy Colour A rare naturally coloured diamond other than white. Can be yellow, green, pink, blue, red or orange.
Fancy Shape Any other shape besides the round brilliant cut.
Fashioning The entire process of manufacturing, i.e. designing, cleaving, sawing, bruting and polishing.
Feather A break or fracture in the stone which may be internal or surface reaching.
Fire Flashes of the different spectral colours seen in a diamond and other gemstones as a result of dispersion.
Fisheye When a diamond’s pavilion is too shallow and as a result a circular reflection of the girdle is seen through the table.
Fluorescence Luminescence occasionally emitted from diamonds when exposed to white light, ultraviolet light or x-rays.
Four C’s Carat, Cut, Colour and Clarity: the four factors determining the quality/value of a diamond.
Fracture A term used to describe the chipping or breaking of a stone along a direction other than cleavage plane.
Fracture Filling Clarity enhancing treatment. High refractive index glass is used to fill in surface reaching fractures. This treatment is not permanent and can be damaged by heat, acid and ultrasonic cleaning.

Gem/Gemstone Mineral or organic material with sufficient beauty, rarity and durability to be set into jewellery.
Gem Gravels Gem gravels are mined from certain alluvial deposits which are, or once were, river beds or lake beds.
Girdle The edge located between the pavilion and the crown which travels around the entire stone.
Goods Generic term used in the diamond business to refer to rough and polished diamonds.
Grain Weight unit equivalent to 0.25 carats.
Graining Irregularities in the crystal structure of a stone which show up as faint lines. As these travel throughout the stone they may be internal or external.

Hardness A stone’s resistance to wear and scratching, measured on Mohs’ hardness scale. Diamond being 10 which is the hardest on the scale.
Heart Shape (H.S.) Modified brilliant cut with a heart-shaped girdle outline.
HPHT Grown Diamonds Diamonds that are synthesized by high pressure and high temperature.
HPHT Treatment (High Pressure High Temperature) A method applied to diamonds to improve, remove or change colour.

Imitation Natural or artificial material that is used to imitate the effects, colour and appearance of other gem materials without possessing their chemical and physical properties.
Inclusion See ‘Clarity Characteristics’.
Industrial Diamonds Non-gem quality diamonds that are only suitable for industrial use (abrasive drills etc.).
Internal Characteristics Imperfections located within the stone.
Internal Reflection The reflection of a feature within a stone.
Irradiated Diamonds Diamonds which are artificially coloured by a bombardment of the atomic structure with radiation.
Isotropic An isotropic material exhibits the same optical properties in all directions through the material. Diamond is isotropic.

Kimberlite Type of igneous diamond-bearing rock. Also known as yellow ground and blue ground.

Lamproite A type of igneous diamond-bearing rock rich in magnesium.
Laser Cut Using a laser to fashion the diamond’s eventual shape, allowing cuts across the growth planes, thus permitting odd shapes such as letters, horse heads etc.
Laser Drilling Treatment often used to reduce the visual impact of dark inclusions. Tiny drill holes are drilled down to the dark inclusion. The dark inclusion can be bleached out by acid to make them lighter. This is a permanent treatment.
Laser Inscription Using a laser to engrave identifying text or numerals, most commonly found on the girdle.
Leverage Gauge Instrument used to measure the precise dimensions of a mounted or unmounted stone.
Loupe Small magnifying glass used in the diamond trade to examine diamonds. Magnification power varies. 10X magnification is specifically used for diamond grading.
Lower Girdle Facet Triangular shaped facets, located on the pavilion.
Lower Main Facet Four sided facets of which there are eight meeting at the centre to form the culet.
Lustre The appearance of a material’s surface in reflected light. Determined by the refractive index and polish, or surface condition.

Make The quality of the symmetry and finish of a polished stone.
Marquise Symmetrical boat shaped brilliant cut with pointed ends.
Master Stones A set of polished stones which have been colour graded to a certain standard by an accredited laboratory for the purpose of colour grading polished diamonds.
Melee Small diamonds of mixed sizes. Both rough and polished.
Microscope An optical instrument that aids visual magnification.
Mohs’ Scale Scale of relative hardness of minerals. The scale runs from 1 to 10 with diamond being the hardest at 10 on the Mohs’ scale.
Moissanite Silicon carbide. Manmade for use in jewellery. Similar in appearance to diamond, may be used as a diamond imitation.

Natural Original surface on the rough diamond crystal left on the polished stone.
Nail Head When the pavilion is too deep, light escapes from the pavilion leaving a dark circle effect under the table.

Oval Modified brilliant cut with an oval shaped girdle outline.

Paste A trade term used to describe any variety of glass gemstone imitation.
Parcel Paper Folded sheets of paper used to contain polished or rough diamonds.
Pavilion The section of the diamond found below the girdle.
Pavilion Facet Four sided facets of which there are eight meeting at the centre to form the culet. (see ‘Lower main facet’)
Pear Shape (P.S.) Asymmetrical cut with one pointed and one rounded end with a pear-shaped girdle outline.
Point Weight unit. One point is 1/100 of a Carat.
Polish The relative smoothness of a surface.
Polished Diamonds Rough stones that have been cut and polished as opposed to rough.
Polishing Lines Small Parallel indentations left on facets during the polishing process.
Princess Cut Modified brilliant cut with a square or rectangular girdle outline.
Proportions The relative symmetry of angles and measurements on a polished diamond.

Quality Term used to describe the overall colour, clarity and cut attributes of a stone.

Raman Spectrometer Used in various applications. Used to detect HPHT treatments in diamonds.
Reflection The bouncing back of light when it strikes an external or internal facet on a polished diamond.
Rejection Polished or rough diamond of very poor quality.
Rough (Stone or Diamond) Gem in its natural form before it undergoes any manufacturing process.
Round Brilliant Cut Most common style of cut for diamonds. A standard round brilliant consists of 57 facets. If there is a culet, 58 facets.

Scaife Flat cast iron wheel upon which diamonds are polished.
Shallow Stone A diamond in which the crown and pavilion are shallow.
Shape The outline of a diamond when viewed perpendicular to the table facet.
Sieve (Diamond-) Round stainless steel plates with perforations which correspond to specified diamond diameters. A quick way to sort small diamonds by size.
Sorting Process of separating rough or polished diamonds into colour, clarity, carat and cut grades.
Star Facet A triangular facet located on the crown of a brilliant cut next to the table, of which there are eight.
Symmetry The accuracy with which the diamond is polished to its perfect proportions.
Synthetic Diamond A manmade diamond having the same physical, optical and chemical properties as a natural diamond.

Table Large facet in the centre of the crown on a polished diamond.
Thermal Conductivity The ability of a material to conduct heat. This principal is used for diamond testers.
Toughness The ability of a material to resist the development of fractures through the material.
Translucent When a material only allows some light to pass through.
Transparent When a material allows most light to pass through.
Treated diamond Diamonds can be treated, other than by cutting, polishing and cleaning, to change the diamonds appearance by coating, filling, heating, irradiation, or any other physical or chemical treatment.
Types Diamonds are split into types according to atomic structure and trace elements. (Type I, Type II)

Ultraviolet (U.V.) Lower end of the light spectrum invisible to the human eye. Ultraviolet light produces fluorescent effects in some materials, which may be an aid to identification or detection.
Upper Girdle Facet Triangular facets located on the lower part of the crown main facet, right above the girdle.

Wavy Girdle A misalignment of the crown and pavilion facets. As a result the girdle is nor parallel with the table.
Weight Weight is measured in carats, subdivided into points.
Well made A well proportioned polished diamond with a good finish.
White A term to describe goods that are D - H colour.

Yield The total carat weight obtained after polishing from the original rough.