Organic gem materials differ from the inorganic materials in that they wre the products of living organisms. With the exception of pearl and coral, these materials are all non-crystalline, which further distinguishes them from the majorirty of inorganic gemstones. Pearls despite their softness are vulnerable to acid attack, perspiration and cosmetics, but saying this have managed to maintain their popularity.  The natural pearl is formed inside a pearl oyster probably as a result of a parasitic lava penetrating the creature's shell causing irritation and infection, the mollusc reacts to this local inflammation by surrounding it with a sac of cells from a protective inner flap of tissue called the mantle or pallium, this sac of mantle tissue in turn secretes a deposit which encapsulate the intruding larva with concentric layers of nacre.  Once a mollusc has enclosed a source of irritation with nacre, it continues to deposit further layers for up to seven years, the thousands of thin tanslucent layers of nacre eventually from a pearl.


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