16 CFR 23.11 - Definition and misuse of the word
(a) A diamond is a natural mineral consisting essentially of pure carbon crystallized in the isometric system. It is found in many colors. Its hardness is 10; its specific gravity is approximately 3.52; and it has a refractive index of 2.42.
(b) It is unfair or deceptive to use the unqualified word “diamond” to describe or identify any object or product not meeting the requirements specified in the definition of diamond provided above, or which, though meeting such requirements, has not been symmetrically fashioned with at least seventeen (17) polished facets.
It is unfair or deceptive to represent, directly or by implication, that industrial grade diamonds or other non-jewelry quality diamonds are of jewelry quality.
(c) The following are examples of descriptions that are not considered unfair or deceptive:
(1) The use of the words “rough diamond” to describe or designate uncut or unfaceted objects or products satisfying the definition of diamond provided above; or
(2) The use of the word “diamond” to describe or designate objects or products satisfying the definition of diamond but which have not been symmetrically fashioned with at least seventeen (17) polished facets when in immediate conjunction with the word “diamond” there is either a disclosure of the number of facets and shape of the diamond or the name of a type of diamond that denotes shape and that usually has less than seventeen (17) facets (e.g., “rose diamond”).
Additional guidance about imitation and laboratory-created diamond representations and misuse of words “gem,” “real,” “genuine,” “natural,” etc., are set forth in §§ 23.23, 23.24, and 23.25.