Pearl is a hard object produced within the soft tissues of a mollusk.

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Pearl is a hard object produced within the soft tissues of a mollusk. Which one of the following is the main constituent of pearl?

Calcium carbonate
Calcium oxide
Calcium nitrate
Calcium sulphate
This question was previously asked in
UPSC CDS-2 – 2017
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The main constituent of pearl is calcium carbonate.
Pearls are formed within mollusks when an irritant, such as a parasite or a piece of shell, enters the shell. The mollusk secretes layers of nacre (mother-of-pearl) around the irritant as a defense mechanism. Nacre is composed primarily of microscopic crystals of calcium carbonate (CaCO3), mainly in the aragonite form, cemented together by an organic protein matrix called conchiolin.
The calcium carbonate layers combined with the organic matrix create the iridescent luster characteristic of pearls. The quality and value of a pearl depend on factors like size, shape, color, luster, surface quality, and nacre thickness.

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