Glossary

Bezel Facet

On a round brilliant diamond, these are eight large kite shaped facets on the crown. Also called the top main facets.

Blemish

Term used in the GIA clarity-grading system for any nick, scratch, abrasion, pit, polish mark, graining or polish line on the surface of a polished diamond.

Brilliance

Intensity of the internal and external reflections of white light from the crown of a polished diamond or other gemstone. Hardness, refractive index, reflectivity, polish, lustre and proportions all affect a gemstone's brilliance.

Brilliant Cut

Cut with a facet arrangement that radiates from the centre of the stone towards the girdle, with triangular or kite-shaped facets. The most common brilliant cut is the round brilliant; modifications include the marquise, half moon, pear shape, heart shape, oval, cushion and antique cushion brilliant cuts.

Carat

Metric carat, the standard unit of weight used for gemstones. One carat equals 0.200 grams (or 200 milligrams). One carat equals 100 points. Usually abbreviated ct.

Cavity

A type of inclusion consisting of a large or deep opening in a diamond.

Chip

Shallow break on a diamond which extends from a facet junction or girdle edge and is larger or deeper than a nick.

Clarity

A gemstone's relative freedom from inclusions and blemishes. Sometimes called purity.

Cleavage

A break in a diamond which is parallel to the diamonds crystal planes. A cleavage may be caused by internal strain or a sharp blow.

Cloud

Hazy or milky area in a diamond; a cloud may be small in area or spread throughout the stone, and may or may not possess a distinct outline.

Colour

Relative position of a diamond's body colour on a colourless-to-light-yellow scale, denoted by standard nomenclature such as letters, numbers, words or a combination thereof. Colour grades are established by comparing a diamond to a set of standard master diamonds under controlled conditions. Such grades are normally assigned only to colourless, near colourless or light yellow, light brown and light gray diamonds; other colours are considered fancy colours and are described differently.

Crown

The area of a diamond above the girdle plane. It consists of the table and the crown facets below it.

Crown Angle

The angle measured between the girdle plane and the bezel facets. Along with table size the crown angle helps determine the amount of dispersion displayed by the diamond.

Crown Height

The part of the diamond above the girdle.

Crown Height Percentage

The crown height expressed as a percentage of the average girdle diameter.

Crystal

A type of inclusion. A crystal is a mineral deposit trapped inside the diamond.

Culet

Small facet on the point of the pavilion of a brilliant-cut diamond or on the keel of a step cut; fashioned to reduce the risk of damage.

Cut

(1) shape and style of a polished diamond, such as a round brilliant or an emerald cut. (2) proportions and finish of a diamond. One of the 4 Cs, also called make.

Depth

The distance between the table and the culet as measured in millimeters.

Depth Percentage

The depth of the diamond divided by the average width expressed as a percentage.

Diamond

Mineral composed essentially of carbon crystallized at extremely high temperatures and pressures; in nature, diamonds form 150 to 200km (93 to 124 miles) or more below the earth's surface. Diamond is the hardest of all known natural substances (10 on the Mohs scale); its refractive index is 2.417, dispersion 0.044, specific gravity 3.52, and its lustre is adamantine. Diamond ranges from colourless to yellow, brown, gray, orange, green, blue, white, black, purple, pink and extremely rarely, red. Transparent and near-colourless is a desirable colour, diamond is a highly valued gemstone.

EGL

European Gemological Laboratory - EGL has franchises in a number of cities around the world which grade diamonds.

Dispersion

Separation of white light into spectral colours, each of which vibrates at a different frequency. Also called fire.

Enhancement

Any post-recovery process which alters the appearance, especially the colour or clarity of a natural diamond or other gem material. Coating, fracture filling, irradiation, heating (annealing) and lasering are all forms of enhancement. Also called treatment.

Eye-Clean

In clarity grading eye-clean diamonds should have no inclusions that are visible through the crown to the unaided eye.

Facet

Flat polished surface on a finished diamond.

Fancy Shape

Any cut other than a round brilliant or single cut. Traditional fancy cuts include the marquise, emerald cut, heart shape, oval shape, pear shape, half-moon, kite, triangle and various modified brilliant cuts.

Fancy Colour

Any naturally coloured diamond with a noticeable depth of bodycolour considered to be rare or attractive. Red and green are the rarest fancy colours, followed by purple, violet, orange, blue and pink. Yellow, sometimes called canary diamonds and greenish yellow diamonds are more common. Light, or low-saturation coloured diamonds other than yellow or brown, may be classed as fancies, but, in the GIA colour-grading system, yellows and browns must be darker than the Z master diamond to merit a fancy grade. Fancy colour grades are decribed as faint, very light, light, fancy light, fancy, fancy intense and fancy dark in the GIA system. Treated diamonds are not considered fancy diamonds, but are sometime referred to as 'treated fancy diamonds' in the trade.

Feather

Cleavage or fracture; may be transparent, but usually has a whitish appearance when seen at right angles to the break. Also called a gletz.

Finish

Quality of a diamond's polish, the condition of its girdle and the precision of the cut.

Fire

See dispersion.

Fisheye

Diamond with a pavilion depth of less than 40 percent, in which a circular gray reflection of all or part of the girdle appears through the table when the stone is examined face-up.

Fluorescence

Emission of visible light by a material such as diamond when it is simulated by higher energy X-rays, ultraviolet radiation or other forms of radiation. Fluorescence continues only as long as the material is exposed to the radiation. Strong or very strong fluorescence may make a diamond appear milky or oily especially in sunlight.

Four C's

The four factors - colour, clarity, cut and carat weight - which determine the value of a diamond.

Fracture

A chip or break on a diamond that is not in the direction of a cleavage plane. Irregular in shape they usually appear step-like.

Fracture Filling

A diamond enhancement process whereby a cavity or opening in a diamond is filled with an artificial substance.

GIA-GTL

Gemological Institute of America Gem Trade Laboratory. Well respected independent laboratory which grades diamonds and includes a diamond grading report with each diamond. GIA is the creator of the 4C's.

Girdle

Narrow band which circumscribes the edge of the plane separating the crown and pavilion of a polished diamond. The girdle can be bruted, faceted or polished.

Girdle Percentage

The measurement describing the percentage of the diamonds average girdle diameter.

Grading Report

Sometimes called a certificate, although labs do not certify diamonds. The grading report issued by an independent laboratory should accurately describe the proportions, weight, colour, clarity, symmetry, polish and fluorescence seen in the diamond being evaluated.

Graining

Visible, shadow-like lines on the surface of, or inside, a diamond, caused by irregularities in the crystal structure. Often a result of twinning or growth defects, grain lines frequently look like polishing lines, except that they can cross facet junctions, while polishing lines cannot; they usually cannot be removed by recutting or polishing. Also called knot lines and twinning lines.

IGI

International Gemological Institute. A laboratory which offers a diamond grading report.

Inclusion

Any of several types of clarity features which are enclosed within a host diamond and they may reach the surface. Some examples are knots, feathers, crystals, needles, clouds and pinpoints.

Knot

Included diamond crystal oriented differently from the larger diamond crystal which is its host. When such diamonds are sawn, the knot may cause problems and slow the sawing process because it often presents a harder cutting direction.

Laser Drill Hole

A tiny tube created in a diamond by a laser drilling.

Laser Drilling

Enhancement process used to improve the appearance of a diamond which contains dark inclusions. A hole is drilled into the diamond with a laser until it reaches the inclusion; if the included material is not vaporized by the laser itself, it is dissolved or bleached with acid.

Length - to - Width Ratio

A comparison of the length and width of the girdle outline on fancy shaped diamonds. The ratio is found by dividing the length of the diamond by the width. The width is always stated as 1.

Loupe

A small magnifying lens used to examine diamonds. 10x magnification is the standard.

Lower Girdle Facets

The facets on the pavilion of a round brilliant just below the girdle.

Master Diamonds

Sets of rough or polished diamonds of known body colour to which other diamonds are compared to judge their colour grade. Master diamonds typically range from colourless through gradually deepening tints of yellow. Also called colour sample or master colour set, master set or masterstones.

Mohs Scale

The 10 point scale of mineral hardness. Diamond scores 10 on the Mohs scale. Diamond is the hardest of all known natural substances.

Nailhead

Round brilliant diamond with a dark centre which resembles the head of a nail; caused by a pavilion depth greater than 48 percent.

Natural

Portion of the original surface or skin, of a rough diamond which is sometimes left on a fashioned stone, usually on the girdle, to indicate that maximum yield has been obtained.

Pavilion

The portion of a polished diamond below the girdle.

Pavilion Angle

The angle measured between the girdle and the pavilion main facet.

Pavilion Main Facets

The eight facets found on the pavilion of a round brilliant diamond.

Pavilion Depth Percentage

The depth of the pavilion in millimeters expressed as a percentage of the average diameter.

Pinpoints

Very small inclusions in a diamond.

Point

A point is 1/100 of a carat. For example a ¼ ct diamond is 25 points and a 1/2ct is 50 points.

Polish

The overall condition of the facet surfaces on a polished diamond.

Proportions

Relative dimensions and angles of a polished diamond and the relationships between them; these include table size, crown angle, crown height, girdle thickness, pavilion angle, pavilion depth, culet size, girdle outline, length-to-width ratio, and total depth.

Shape

Face-up girdle outline of a polished diamond or other gem, such as round brilliant, pear, marquise, heart, oval or square.

Star Facet

One of eight triangular facets found on the upper crown section, next to the table of a brilliant cut diamond.

Symmetry

Grading term for the exactness of shape and placement of facets. Faults affecting symmetry include off-centre culets and tables, poor facet alignment, misshapen facets, out-of-round girdles and wavy girdles.

Table

Large facet in the centre of the crown of a polished diamond.

Table Percentage

The width of the table divided by the average diameter.

Upper Girdle Facets

One of the 15 facets found on the lower crown portion of the diamond.