Pearls from theREDjewelrybox.com

Pearls have been treasured for their splendor and rarity for over than four thousand years. All around the world pearls have been valued longer than any other gem. They are the only gemstones grown from a living organism.

When a foreign substance (most often a parasite - not a grain of sand) are introduced within the oysters or mollusks Pearls are made. This foreign substance enters the soft mantle tissue and in resonse 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.