Glossary of Diamond Terms and Abbreviations

The diamond industry encompasses physics, chemistry, maths, art, nature, history, construction…in fact, it is so very broad and so very complex that it is understandable that many are left baffled by industry specific jargon. If you are puzzled by pavilions and confused by culets, this glossary of terms will help you understand the definitions of these terms as well as the shorthand that is often used in the diamond business.

General Terms:

AGS/AGSL – American Gem Society Laboratory

ASET – Angular Spectrum Evaluation Tool, the graphical foundation of the AGS light performance cut grading system. A hand-held reflector device used to assess light leakage

Azimuth – A measurement of the direction that a facet is pointing

Baguette – An elongated step cut

Blocking – A preliminary step in diamond cutting where the basic proportions and symmetry of the diamond are established and the first 8 facets on both crown and the pavilion are placed.

Bezel – The main crown facets

Boron – The chemical element that gives natural blue diamonds their color

Carat – A unit of weight: 1.00 carat = .20 grams. Derived from the word ‘Carob’ – the seeds originally used to weight diamonds against

Certificate – Common term for a gem lab report

Clarity – The clarity grade of a diamond

Color – The color grade of a diamond

Chevrons – V shaped sets of facets on the pavilion of a princess cut

Crown – The proportion of the diamond above the girdle

Crown Angle – The angle created by the intersection of the girdle and bezel facet

Crown Height – The measurement extending from the girdle to the table

Culet/Cul – The tip of the pavilion. Either pointed or as an additional facet

Cut – The cut grade, determined the proportions and facets of the diamond and light performance

Depth/Dpth – The measurement from the table to the culet

Depth Percentage – The depth of the diamond in relation to the average diameter

Dossier – GIA issued documents in lieu of a full certification. Given to diamonds under 1.00ct

DQD – AGS diamond quality document

EGL – European Gemological Laboratory

Eye Clean –  A diamond where inclusions cannot be seen when examined with the naked eye

EX – GIA Excellent

F – Faceted girdle

Facet – The flat polished surfaces of a diamond

Face Up – Viewing the diamond through the table

Fancy Color – Intense colours outside the normal D-Z range

Fancy Shape – Any diamond that is not round

FB – Faint blue fluorescence

Flr – Fluorescence rating of the diamond

Fluorescence – After being exposed to UV light some diamonds may emit colored light in varying degrees of intensity. Fluorescence is measured as it can impact on the appearance and price of a diamond

FT – Faint fluorescence

GIA – Gemological Institute of America

Girdle – A vertical plane around the perimeter of a diamond. Will vary in thickness and can be faceted, polished or unpolished

H&A – Hearts and arrows patterning; the result of a high precision cut on a round brilliant diamond

Hardness – Resistance to scratching, measured using the Mohs Scale

HCA – The Holloway Cut Advisor tool

Ideal – A term for a diamond with Zero Ideal cut proportions

IF – Internally flawless

In-house – A diamond immediately available for purchase (as oppose to virtual)

Ins – Inscribed. Usually on the girdle with a serial number or brand name

Keel – The equivalent of a culet in non-brilliant style facet arrangements. A line on the bottom pavilion instead of a point

Lower Girdle – The pair of facets below the girdle and between the pavilion mains

Leakage – Light that enters the crown and is not returned to the eye

Light Return – Light that is reflected back to the eye resulting in brightness

Loupe – An eye-glass tool used by jewellers. A standard loupe offers 10x magnification

M – Girdle – The girdle thickness is Medium

Marquise – An elliptical diamond shape

MB – Medium Blue Fluorescence

Melee – Small accent diamonds used in jewelry

Moissanite – A modern, synthetic diamond material

M-SK – Medium to Slightly Thick Girdle

M-SK-F – Medium to Slightly Thick, Faceted Girdle

M-TK – Medium to Thick Girdle

M-TK-F – Medium to Thick, Faceted Girdle

N – Culet – None or too small to measure

N – Fluorescence – None, Inert, Nil

N – Girdle – Thin Girdle

N-F – Thin, Faceted Girdle

N-M – Thin to Medium Girdle

N-M-F – Thin to Medium, Faceted Girdle

N-SK – Thin to Slightly Thick Girdle

N-SK-F – Thin to Slightly Thick, Faceted Girdle

Opal – A brilliant cut – round and elongated shape

Origin – The country where the rough diamond was mined

Pave – Small diamonds set very close together to created a fully ‘paved’ appearance

Pavilion – The portion of diamond below the girdle

Pavilion Angle – The angle created by the intersection between the girdle and main pavilion facet

Pear – A brilliant cut featuring a pointed top and a rounded lower half

Polish – A mirror effect on the facets of a diamond

Prop – Proportions rating of the diamond as specified by the AGS Laboratory or as determined by Sarin Computerized Proportions Analysis

Sarin – Computerized Proportions Analysis used by most laboratories to determine the proportions of the diamonds that they grade

SB – Strong Blue Fluorescence

Size – Carat Weight

SK – Slightly Thick Girdle

SK-F – Slightly Thick, Faceted Girdle

SK-TK-F – Slightly Thick to Thick, Faceted Girdle

Star – The triangular facets between the table and the upper girdle facets

Step Cut – A diamond cut feature square or rectangular shapes

Sym – The symmetry grade given by a gem lab

Symmetry – The precision and uniformity of facet alignment

Table – The largest facet on the crown of the diamond

Tolkowsky – The pioneer of the ideal cut for a round brilliant diamond

Tolk-0 – EGL Tolkowsky cut diamond with ideal cut proportions

Upper Girdle – The pairs of facets above the girdle and between the crown mains

VG – Very Good (very difficult to locate under 10x magnification)

VN – Very Thin – Girdle.

VS – Very Small – Culet

VSB – Very Strong Blue Fluorescence

Diamond Clarity Terms

Abrasion – An area of unpolished surface that is the result of wear and tear

Bearded Girdle – A series of feathers formed at the girdle as a result of the cutting process

Bruise – An area of impact with tiny feathers. Usually seen at a facet junction

Carbon – A dark group of crystals within the diamond

Cavity – An angular opening normally caused by a part of a feather breaking away or when a surface-reaching crystal drops out

Chip – External damage to the surface of the stone

Cloud – Areas of pinpoints that can vary in density

Crystal – A mineral crystal that has formed within a diamond

Extra Facet – An additional facet that is normally there to hide an inclusion or repair damage

Feather – Clarity feature with a white, feathery appearance caused by separation in the lattice of the diamond

Indented natural -A portion of the rough diamond’s original surface

Knot – An included crystal that reaches the surface of the diamond

Laser Drill – A tunnel that reaches of the surface of the diamond. The appearance is thread-like

Natural – A piece of rough diamond left on the stone to maintain weight

Needle – A thin, elongated crystal inclusion

Nick – Similar to a surface level chip but with less depth

Pinpoint – A very tiny crystal that present as a dot

Pit – A tiny white dot

Polish lines – Ridges and lines left on the surface of a diamond as a result of the polishing process

Polish marks – A cloudy white film on the surface of a facet – the result of overheating during the polishing process

Surface Graining – Grain lines seen on a facet’s surface

Twinning Wisp – Series of pinpoints, clouds, or crystals that forms in a diamond’s growth place

Richard Jenkins, The Diamond Guru

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