Diamond Terminology
A-C
Brilliance: White light reflected back to the eye from the interior and surface of a diamond. Determined primarily by cut quality.
Carat (ct): The unit of weight used for diamonds. One carat equals 0.2 grams or 200 milligrams.
Certification: An independent assessment of a diamond's characteristics (4 C's and measurements) issued by a gemological laboratory such as IGI or GIA.
Clarity: A grading of the relative absence of inclusions and blemishes in a diamond. Scale: FL, IF, VVS1, VVS2, VS1, VS2, SI1, SI2, I1, I2, I3.
Crown: The upper portion of a diamond, above the girdle.
Culet: The small facet at the very bottom point of a diamond's pavilion. Ideally, it should be very small or pointed (no culet).
Cut: The quality of a diamond's proportions, symmetry, and polish - the factor with the greatest influence on a diamond's visual beauty.
CVD (Chemical Vapour Deposition): A method of growing diamonds by depositing carbon atoms from a gas onto a diamond seed in a vacuum chamber.
D-F
Depth: The height of a diamond from table to culet, expressed as a percentage of the diameter.
Dispersion: The separation of white light into spectral colours as it passes through a diamond. Also called "fire".
Eye-clean: A diamond that has no inclusions visible to the unaided eye. Generally, VS2 and above are considered eye-clean.
Facet: A flat, polished surface on a diamond. A round brilliant has 57 or 58 facets.
Fire: Coloured flashes of light produced when white light is dispersed into spectral colours by a diamond's facets.
Fluorescence: The visible light some diamonds emit when exposed to ultraviolet (UV) light. Graded from None to Very Strong.
G-L
GIA: Gemological Institute of America - one of the world's most respected independent gemological laboratories.
Girdle: The narrow band around the widest circumference of a diamond, separating the crown from the pavilion.
HPHT (High Pressure High Temperature): A method of growing diamonds by subjecting carbon to extreme pressure and temperature, mimicking natural diamond formation conditions.
IGI: International Gemological Institute - a leading independent gemological laboratory widely used for certifying lab-grown diamonds.
Inclusion: A natural characteristic enclosed within a diamond, such as a crystal, feather, or cloud. Inclusions affect clarity grade.
Lab-grown diamond: A genuine diamond created in a controlled laboratory environment using HPHT or CVD technology. Chemically and physically identical to a mined diamond.
M-S
Mohs scale: A scale of mineral hardness from 1 (softest, talc) to 10 (hardest, diamond).
Pavilion: The lower portion of a diamond, below the girdle.
Point: A unit of diamond weight equal to 1/100th of a carat. A 50-point diamond weighs 0.50 carats.
Polish: The quality of the surface finish on a diamond's facets. Graded from Excellent to Poor.
Scintillation: The pattern of light and dark areas, and the flashes of white light, visible when a diamond, the light source, or the viewer moves.
Step cut: A faceting style with long, rectangular facets arranged in parallel rows (e.g., emerald, Asscher, baguette cuts).
Symmetry: The precision of a diamond's facet alignment, proportions, and overall shape. Graded from Excellent to Poor.
T-Z
Table: The large, flat facet on the top of a diamond. Table percentage is the table width relative to the diamond's diameter.
Total depth: The measurement from the table to the culet, typically expressed as a percentage of the average diameter.