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| Various forms of Pearls |
Pearls are formed inside the shell of live pearl oyster (e.g. Pinctada). They come
under the animal group known as Mollusca. In Mollusca, there is a sub group called Bivalvia in which these animals belong.
Pearl oysters have a hard shell covering their body. This shell is made up of calcium carbonate. ln between the shell and its body there is an empty space. It is called mantle cavity.
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| Pearl inside pearl oytser |
Actually, a natural pearl begins its life as a foreign structure like a parasite or piece of shell that accidentally lodges inside the mantle. This foreign structure cannot be expelled. It irritates the oyster. To avoid this, the oyster’s body continuously secretes a smooth, hard crystalline material around the irritant. This substance is known as nacre. Chemically, nacre is microscopic crystals of calcium carbonate. When light is passed along the axis of one crystal, it is reflected and refracted by another producing a rainbow of light and colour.
Slowly, the irritant is completely encased forming a beautiful pearl.
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