FTC Guides on Diamonds

Diamonds

A diamond’s value is based on four criteria:

Color often is graded on a scale established by the Gemological Institute of America (GIA). On the GIA scales, color is rated from D to Z, with D at the top.
Cut refers to the quality of how the diamond has been shaped, taking into account the diamond’s proportions, polish, and symmetry.
Clarity measures the natural imperfections in the stone. On the GIA scales, clarity is rated from flawless to I3. A diamond can be described as “flawless” only if it has no visible surface or internal imperfections when viewed under 10-power magnification by a skilled diamond grader.
Carat refers to the stone’s weight.

Diamond weight usually is stated in carats and may be described in decimal or fractional parts of a carat. If the weight is given in decimal parts of a carat, the figure should be accurate to the last decimal place. For example, ”.30 carat” could represent a diamond that weighs between .295 and .304 carat. Some retailers describe diamond weight in fractions, using the fraction to represent a range of weights. A diamond described as 1/2 carat could weigh between .47 and .54 carat. If diamond weight is stated as fractional parts of a carat, the retailer should disclose two things:

that the weight is not exact
the reasonable range of weight for each fraction or the weight tolerance being used

Diamonds