16 CFR 23.18 - Definitions of various pearls.
As used in these guides, the terms set forth below have the following meanings:
(a) Pearl: A calcareous concretion consisting essentially of alternating concentric layers of carbonate of lime and organic material formed within the body of certain mollusks, the result of an abnormal secretory process caused by an irritation of the mantle of the mollusk following the intrusion of some foreign body inside the shell of the mollusk, or due to some abnormal physiological condition in the mollusk, neither of which has in any way been caused or induced by humans.
(b) Cultured pearl: The composite product created when a nucleus (usually a sphere of calcareous mollusk shell) planted by humans inside the shell or in the mantle of a mollusk is coated with nacre by the mollusk.
(c) Imitation pearl: A manufactured product composed of any material or materials that simulate in appearance a pearl or cultured pearl.
(d) Seed pearl: A small pearl, as defined in (a), that measures approximately two millimeters or less.