SeaWater Pearl

A pearl is not a mineral in the ordinary sense but an organic gem, built by a mollusc from layer on layer of nacre, microscopic platelets of aragonite, a form of calcium carbonate, cemented by the protein conchiolin, deposited around an irritant inside the shell. The interference of light in those thin layers produces the soft internal glow called orient.

Saltwater pearls from marine oysters were historically the most valued, and natural pearls, formed without human intervention, were among the costliest of all gems before the twentieth century, when Kokichi Mikimoto's perfecting of culturing around 1900 made bead-nucleated pearls widely available and collapsed the value of the natural stone. In Indian jyotisha the pearl is the primary gem of the Moon, Chandra, and one of the navaratna; across many cultures it has symbolised purity and the moon. Because pearl is soft, hardness about 2.5, and dissolves in acid, it is the most delicate of gems.

The natural pearl was, until roughly a century ago, one of the most valuable things a person could own, and the reason was that the supply came from diving.

The great historical fisheries were the Persian Gulf, worked from the Arabian shore, and the Gulf of Mannar between southern India and Sri Lanka, with a further fishery in the Red Sea and, after the sixteenth century, in the Caribbean and off Venezuela. The Gulf fisheries were organised by season, worked by breath-hold divers from open boats, and the human cost was extreme and well documented by the seventeenth century travellers, among them Tavernier, who recorded the operation in detail.

A natural pearl forms when an irritant becomes lodged in the mantle of a mollusc and is coated in nacre. It is a rare accident. Estimates of how many oysters must be opened for one saleable pearl run into the thousands, and the yield could not be improved by effort. That is the whole economic basis of the pearl's status, and it is entirely different from the basis of a mined gem's value.

The cultured pearl ended it. Once a pearl could be induced reliably, the price of the natural article collapsed and the Gulf economies that had depended on the fishery were devastated within a decade, in the same period that oil was found beneath them.

Sea-water or saltwater pearls are distinguished in the modern trade from freshwater pearls by their origin and by the culturing method used, and the distinction now carries most of the market value that the natural and cultured distinction once did.