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Diamond glossary

44 terms from grading reports and jeweler counters, defined in a sentence or two, linked to the guides that use them.

A

AGSlab
American Gem Society. Its laboratory grades cut on a 0–10 scale, where 0 is Ideal; known for light-performance analysis such as ASET imaging.The 4Cs of Diamonds
ASETtool
Angular Spectrum Evaluation Tool. A colour-coded image showing where a diamond gathers light and where it leaks it.The 4Cs of Diamonds
Asscher cutshape
A square step cut with cut corners and a deep pavilion, producing a 'hall of mirrors' look.

B

Bow-tiecut
A dark area shaped like a bow tie across the centre of elongated shapes such as ovals, pears and marquises.The 2026 Diamond Trend Report
Brilliancelight
The white light a diamond returns to the viewer. Driven mainly by cut proportions.The 4Cs of Diamonds

C

Carat4Cs
A unit of weight: 1 carat = 200 milligrams = 0.2 grams. It measures weight, not size.The 4Cs of Diamonds3 Carat Diamond Price Guide 2026
Clarity4Cs
How free a diamond is from inclusions and blemishes, graded from Flawless (FL) to Included (I3) under 10× magnification.VS1 vs VS2 Diamond Clarity
Colour4Cs
For white diamonds, the absence of colour, graded D (colourless) to Z (light yellow or brown) on the GIA scale.Diamond Color Grade Chart
Crownanatomy
The upper part of a diamond, above the girdle, containing the table and crown facets.
Culetanatomy
The point or small facet at the bottom of the pavilion. 'None' or 'Pointed' is standard on modern rounds.
Cut grade4Cs
A grade for how well a diamond's proportions, symmetry and polish handle light. GIA's top grade for rounds is Excellent; AGS's is Ideal (0).The 4Cs of Diamonds
CVDlab-grown
Chemical vapour deposition. Diamond is grown layer by layer from a carbon-rich gas onto a diamond seed plate.Lab Grown Diamonds

D

Depth %proportion
Total depth divided by average diameter. Rounds commonly sit around 59–63%.The 4Cs of Diamonds
Dispersionlight
The splitting of white light into spectral colours, seen as 'fire'. Diamond's dispersion is 0.044.Moissanite vs. Lab Grown Diamond

E

Emerald cutshape
A rectangular step cut with long parallel facets and cut corners. Shows clarity more openly than brilliant cuts.
Eye-cleanclarity
No inclusions visible to the unaided eye at normal viewing distance. Not a lab grade; it must be checked per stone.VS1 vs VS2 Diamond Clarity

F

Fancy colourcolour
Diamonds with colour beyond the Z range or in other hues (blue, pink, yellow), graded on a separate scale.Blue Diamonds
Firelight
The flashes of spectral colour produced by dispersion.
Fluorescencecolour
A glow, usually blue, under ultraviolet light. Graded None to Very Strong; strong fluorescence can make some stones look hazy.

G

GIAlab
Gemological Institute of America. Created the 4Cs and the D–Z colour scale; the reference lab for natural diamonds.The 4Cs of DiamondsWhat Exactly Is an IGI Certified Diamond?
Girdleanatomy
The narrow band around a diamond's widest point, where report numbers are often laser-inscribed.

H

Hearts and arrowscut
A pattern seen through a special viewer in precisely cut rounds: eight arrows face-up, eight hearts face-down.The 4Cs of Diamonds
HPHTlab-grown
High pressure, high temperature. A growth method that recreates mantle-like conditions; also used to treat colour.Lab Grown Diamonds

I

IGIlab
International Gemological Institute, founded in Antwerp in 1975. Grades a large share of laboratory-grown diamonds.What Exactly Is an IGI Certified Diamond?
Inclusionclarity
A feature inside a diamond, such as a crystal, feather or cloud, formed during growth.VS1 vs VS2 Diamond Clarity

L

Lab-grown diamondlab-grown
Diamond crystal produced in a laboratory by HPHT or CVD, with the same chemical and optical properties as natural diamond.Lab Grown DiamondsThe 50% Tipping Point
Loupetool
A small magnifier; the 10× loupe is the standard for clarity grading.5 Tools You Need to Inspect a Diamond Like a Pro

M

Magic weightscarat
Round-number weights such as 0.50, 1.00 and 1.50 ct, where price per carat jumps. Stones just below cost noticeably less.The 4Cs of Diamonds
Marquiseshape
A boat-shaped brilliant with pointed ends; long and spreads well for its weight.
Moissanitesimulant
Silicon carbide. Not a diamond: it is doubly refractive and shows stronger, more colourful fire.Moissanite vs. Lab Grown Diamond

O

Ovalshape
An elongated brilliant. Faces up larger than a round of the same weight; watch for a bow-tie.The 2026 Diamond Trend Report

P

Pavilionanatomy
The lower part of a diamond, below the girdle. Its angle largely decides whether light returns or leaks.The 4Cs of Diamonds
Pearshape
A teardrop-shaped brilliant combining a round end and a point.
Princess cutshape
A square or near-square brilliant with pointed corners.

R

Radiant cutshape
A rectangular or square shape with cut corners and brilliant faceting.
Rapaportmarket
A widely used wholesale diamond price list that dealers trade against, usually at a discount.RapNet AlternativeCurrent Diamond Prices
Refractive indexlight
How strongly a material bends light. Diamond's is 2.42.
Round brilliantshape
The 57- or 58-facet round cut engineered for maximum light return; the most popular shape.The 4Cs of Diamonds

S

Scintillationlight
The sparkle pattern of light and dark flashes as the diamond, light or viewer moves.
SI1 / SI2clarity
Slightly included. Inclusions are noticeable under 10× and sometimes, especially in SI2, to the eye.VS1 vs VS2 Diamond Clarity

T

Tableanatomy
The large flat facet on top. Table % is its width relative to the stone's diameter.
Tennis braceletjewelry
A flexible line bracelet of evenly matched diamonds.Diamond Tennis Bracelet 2026

V

VS1 / VS2clarity
Very slightly included. Minor inclusions that are difficult (VS1) to somewhat easy (VS2) to see under 10×.VS1 vs VS2 Diamond Clarity
VVS1 / VVS2clarity
Very, very slightly included. Inclusions so slight they are difficult for a skilled grader to see under 10×.VS1 vs VS2 Diamond Clarity