Saturday, August 30, 2008

Natural Pearls

Pearls have been prized for their beauty and rarity for more than four thousand years. From ancient China, India, and Egypt, to Imperial Rome, to the Arab world, to Native American tribes, cultures from around the world and throughout recorded history have valued pearls longer than any other gem.Pearls are the only gemstones grown inside of a living organism. Pearls are formed within oysters or mollusks when a foreign substance (most often a parasite - not a grain of sand) invades the shell of the mollusk and enters the soft mantle tissue. In response to the irritation, the mantle's epithelial cells form a sac (known as a pearl sac) which secretes a crystalline substance called nacre, the same substance which makes up the interior of a mollusk's shell, which builds up in layers around the irritant, forming a pearl.
There are approximately 8,000 different species of bi-valve mollusks, of which only about 20 are capable of consistently producing pearls. Natural pearls are extremely rare. Because the layers of nacre tend to maintain the irregular shape of the original irritant, natural pearls which are round or spherical in shape are even more rare. Most natural pearls are irregularly shaped.
In a completely natural state, only a very small percentage of mollusks will ever produce a pearl and only a few of them will develop a desirable size, shape, and color; only a small fraction of those will be harvested by humans. It is commonly assumed that one in ten thousand mollusks naturally produce gem quality pearls. Obviously, if we relied only on nature, ownership of pearls would still be relegated to the wealthiest and pearl producing mollusks would be on the brink of extinction due to over-harvest. As pearls have been prized for thousands of years, this need has led to the development of cultured pearls.