Pearl is the June birthstone
Modern birthstone for June: Pearl
Traditional Birthstone for June: Alexandrite
Mystical birthstone for June: Moonstone
Hindu/Indian birthstone for June: Pearl
Also for these Sun Signs or Zodiac
Pearls consist of about 92 percent of calcium carbonate, or CaCo3, in the form of aragonite crystals, held together by an organic substance, conchiolin (about 6 percent), which is identical to the horny outer layer of oyster shells, plus a small quantity of water (about 2 percent). Mother-of-pearl has a similar chemical composition, but with less calcium carbonate (about 66 percent) and more water (about 31 percent) and is used as the nucleus of cultured pearls. Pearls are undoubtedly the most costly and important of “organic” gems. They have been known since time immemorial in the Orient and were known to the Greeks and Romans, evidently following the conquests of Alexander the Great.
All manner of fantastic explanations for the origins of pearls were advanced in earlier times, some of them highly poetic. There is, for example, the old eastern legend quoted by Pliny, according to which oysters rose to the surface of the sea beneath the moon’s rays, opened their shells and were fertilized by drops of dew. It was not until the mid-sixteenth century that a Dutch scholar by the name of Rondoletius recognized that pearls were pathological formations in pearl oysters.
Physical properties: Pearls have a hardness of 2.5-4.5; but they are fairly resilient, due to the organic substance they contain and their compact, concentrically layered structure. The density varies from 2.40 to 2.80 g/cm3, but most of those used as gems have a density of about 2.68-2.74 g/cm3 in the case of natural pearls and 2.73-2.78 g/cm3 in the case of cultured pearls. The refractive index can only be measured by complex procedures.
Genesis: Pearls form when a foreign body, such as a grain of sand, or more often a small parasite, finds its way into a pearl oyster which, in self-defense, surrounds the intruder with a cyst, and goes on depositing layer after layer of pearl over it, even when the intruder has been completely encapsulated and rendered incapable of doing any harm. Many mollusks produce pearls, but the most important ones belong to different species of the genus Pinctada (formerly known as Me/eagrina), including P. margarititera, P. maxima, P. martensi, P. fucata, and P. vulgaris. These are medium-large bivalve mollusks (about 25 cm) of the Pteriidae family (Filibranchia order).
Less valuable pearls are produced by many other mollusks, including some freshwater bivalves and marine gastropods. Ever since antiquity efforts have been made to speed up the natural processes of pearl formation and obtain more, bigger, and better-shaped pearls from oysters. The first serious attempts apparently date from the twelfth century, when the Chinese devised a method according to which variously shaped objects—typically images of Buddha were placed between the mantle and shell of certain types of mollusk; after a couple of years it would be covered with a layer of mother-of-pearl.
The production of cultured pearls, however, was pioneered in Japan around the turn of the twentieth century, by Mikimoto, who achieved the first positive results in 1893 with the production of blister pearls; by Mise, who set up production in 1907; and finally by Nishikawa and Mikimoto, to whom we owe the present method of cultivation, which dates from 1919. Briefly, the procedure consists of cutting a small piece of mantle out of a live oyster, wrapping it around a mother-of-pearl bead, and inserting it into the living tissue of another oyster. The oysters thus treated are placed in cages suspended from rafts in calm waters, at variable depths depending on the seasons, to ensure a temperature of not less than 50°F. The depths usually range from 2 to 3 meters in spring-summer and 5 to 6 meters in autumn-winter, thus achieving a balance, over the course of a year, between the effects of shallow water, conducive to rapid growth, and greater depth, which enables the pearls to acquire better color and luster.
The pearls can be harvested after five to seven years, but better results are achieved with longer periods of up to twelve years. Much shorter periods of growth—even less than half—are being used in another center of production which is developing alongside the famous Japanese industry, in areas of northern-western Australia, where the average temperatures are higher.
Occurrence: The largest quantities of pearls are harvested from Sri Lanka, the Philippines, China, Japan, northern Australia, the Persian Gulf, and the Red Sea. Pearl production in the Americas is less important and is mainly confined to the Gulf of California and the Caribbean.
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