The language
of diamonds.
Every grade, cut and market term you'll meet on DiamondTheGuide — explained in plain words, with an illustration where a picture helps.
Browse by topic or letter below
Start here: the 4Cs
The four grades that set most of a diamond's price
The price a seller lists a stone for. DiamondTheGuide's prices are medians of asking prices, not final sale prices.
Illustrated →A square step cut with deeply cropped corners, giving a concentric look from above.
Illustrated →A surface feature such as a scratch, nick or polish line. Counted in clarity along with inclusions.
Illustrated →A darker band across the centre of some elongated brilliants, such as ovals and pears.
Illustrated →A faceting style built from triangular and kite-shaped facets to maximise sparkle.
The unit of weight for gemstones: 1 carat equals 0.2 grams. It measures weight, not face-up size.
Illustrated →How colorless the diamond is, graded from D (colorless) to Z (light yellow or brown).
Illustrated →The point or tiny facet at the very bottom of the pavilion. Modern stones have None or Very Small — a large culet appears as a dark circle through the table.
Illustrated →How well proportions, symmetry and polish return light. GIA grades standard round brilliants Excellent to Poor.
Illustrated →Chemical vapour deposition: a way of growing diamond layer by layer from carbon-rich gas.
Illustrated →Total depth of the stone divided by its average diameter, as a percentage.
A rectangular step cut with long parallel facets. Its open table makes clarity easy to see.
Illustrated →No inclusions visible to the unaided eye at normal distance. A useful description, not an official grade.
A flat, polished surface on a cut gemstone.
Any diamond shape other than round.
A glow, often blue, under ultraviolet light. Graded None to Very Strong. Can make lower-colour stones look whiter — or very rarely cause haziness in colourless ones.
Illustrated →Gemological Institute of America — the non-profit lab that created the D–Z colour and FL–I3 clarity scales. Its reports are the industry gold standard for natural diamonds.
Illustrated →The narrow edge around the widest part of the stone, where crown meets pavilion. GIA grades thickness from Extremely Thin to Extremely Thick — both extremes affect durability or cut grade.
Illustrated →A lab document recording a stone's grades and measurements under a unique report number.
Illustrated →High pressure, high temperature: a method of growing diamonds, also used as a treatment to change color.
International Gemological Institute, a grading lab widely used for lab-grown diamonds.
A feature inside a diamond, such as a crystal, feather, cloud or pinpoint.
Real diamond grown in a factory. The same material as natural, but priced as a separate market.
How much cheaper lab-grown is than natural for the same shape, size and grades.
How elongated a fancy shape is — length divided by width, such as 1.40 for an oval.
A small hand magnifier. Clarity is graded at 10× magnification.
Popular carat weights — 0.50, 1.00, 1.50, 2.00 ct — where price per carat jumps noticeably. Buying just below a magic size is one of the most effective ways to get more stone for the money.
Illustrated →The middle value of a sorted list. DiamondTheGuide uses it because a few extreme prices can't drag it.
A diamond formed in the earth over millions to billions of years and then mined.
An elongated brilliant that looks larger per carat than a round of the same weight.
The lower, cone-shaped part of a diamond, below the girdle.
The grade for how smooth the facet surfaces are.
Total price divided by carat weight — the trade's working unit for comparing stones.
A square brilliant with pointed corners, usually protected by prongs.
A weekly subscription benchmark of diamond asking prices. Dealers quote trades as a percentage discount from "Rap" — typically −25% to −70% depending on grade and demand.
Illustrated →The most popular shape, with 57 or 58 facets arranged for maximum brightness.
The range where most listings sit — between the 25th and 75th percentile price.
Rows of parallel, rectangular facets that give broad flashes of light rather than sparkle.
The grade for how precisely a diamond's facets are shaped, aligned, and positioned relative to each other. Graded Excellent to Poor — both symmetry and polish must be Excellent for a Triple-Ex designation.
Illustrated →The large, flat facet on top of the stone.
Table width as a percentage of the stone's average diameter.
A process that changes appearance, such as fracture filling. Treated stones are left out of DiamondTheGuide's prices.