Pearl
An organic gem grown by molluscs — soft, lustrous nacre requiring gentle care.
Also known as: Nacre
intermediate Cultured in molluscs
What it is
Pearl is an organic gem produced inside molluscs when the animal deposits concentric layers of nacre — aragonite (a form of calcium carbonate) bound by the protein conchiolin — around an irritant. Its overlapping platelets diffract light to create the characteristic soft lustre and orient (iridescence). Pearl is very soft at 2.5 to 4.5 on the Mohs scale and sensitive to acids, heat and cosmetics.
Most pearls sold today are cultured: a bead or tissue nucleus is deliberately inserted to seed nacre growth, in freshwater mussels or in saltwater oysters that yield Akoya, South Sea and Tahitian pearls. Natural pearls are rare and historically very valuable. Pearls should be wiped after wear, kept from chemicals, and stored separately from harder gems.