Clarity

The degree to which a diamond is free from internal characteristics and blemishes. Clarity is graded on a scale from Flawless (FL) to Imperfect (I).

Cleavage

A crack in a diamond which is parallel to one of its crystallographic planes. A cleavage may be caused by inherent internal strain or by a sharp blow. The crack usually extends to the surface.

Cloud

A group of minute to very small, white inclusions which give a "cloudy" appearance.

Crown

The part of the diamond that is above the girdle. 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 the table size, the crown angle helps determine the amount of dispersion (also called "fire") displayed by the diamond.

Crown Height

The part of the diamond that is above the girdle.

Crystal

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

Culet

The point at the bottom of a full-cut diamond. Some diamonds have a faceted culet.

Cut

The cut (or make) of a diamond refers both to the proportions and the finish of a polished diamond. The cut is the most important of the 4Cs (cut, color, clarity, carat) in determining the diamond’s overall beauty, and is the only man-made contribution to a diamond's beauty and value.

Depth

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

Depth Percentage

Also called "total depth", this figure is expressed in % and is the result of the following calculation:

• Round-shaped diamond: the diamond’s depth (mm) divided by its average diameter (mm).
• Fancy-shaped diamond: the diamond’s depth (mm) divided by its width (mm).

Facet

The polished planes on the surface of a gemstone.

Feather

A fracture or break in a diamond that looks like a white feather.

Fluorescence

The property in approximately 50% of all diamonds that makes them glow when exposed to ultraviolet light (such as the lighting frequently seen in night clubs). Diamonds can fluoresce in a number of colors, but blue fluorescence is most common. Depending on its intensity, blue fluorescence may enhance the color of some diamonds by hiding their yellow tint.

Fracture

A chip or break on a diamond that is not in the direction of a cleavage plane

Girdle

The outer edge, or outline, of the diamond's shape. This is the area where the average diameter, width and length of stones are measured. The girdle is situated in-between the pavilion (lower part) and the crown (upper part). It can be faceted, polished or unpolished in which case it looks granular.

Girdle Thickness

The measurement describing the girdle thickness is the average distance between the pavilion (lower part) and crown (upper part), measured in millimeters but usually expressed in percentage of the average diameter.

Hearts & Arrows (Pattern)

"Hearts & Arrows" are usually (but not necessarily) Excellent-Ideal cuts of superior quality. Polishers used "secret recipes" to create the pattern of "Hearts" looking down through the pavilion and "Arrows" seen in the table-up position. The precision and sharpness of the patterns relied on precise angles in combination with specific facet length, width and azimuth.

Inclusion

A naturally occurring imperfection in a diamond, commonly referred to as "internal characteristic". Some examples are: feathers, crystals, needles, clouds and pinpoints.

Laser Inscription

Is the laser-etched text put on the girdle of a diamond for identification purposes. Usually the text is the laboratory initials (IGI) and the grading report number.

Lower-Girdle Facet

Also called "lower halves", they are the facets on the pavilion of a round brilliant just below the girdle.

Luster

The degree to which a diamond or gemstone reflects light.

Natural

A small rough diamond portion that can be found on some polished diamonds. This is often done so the polisher can maximize weight yield of a diamond.

Pavilion

The lower part of a polished diamond, usually cone-shaped.

Pavilion Angle

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

Pinpoint

Internal characteristic: minute to very small, usually a whitish dot inside a diamond.

Star Facet

One of the eight triangular facets found at the edge of the table facet and pointing to the outline of a brilliant-cut diamond.

Symmetry

Symmetry of individual facets, and symmetry of the parts of the stone as well as their overall alignment, is what a gemologist must observe and grade from "Excellent" to "Poor".

Table

The largest facet, situated on top of the crown of a diamond. This is where most of the light enters and exits a diamond.

Table Percentage

The width of the table divided by the average diameter.

Upper-Girdle Facet

Also called "upper halves", they are the 16 facets found on the crown, between the girdle and the star facets.