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from Mount Vesuvius, Siberia, Germany, Norway and California.
26. Zoisite belongs to the epidote group, orthorhombic. Colour: grey, greenish or red. The manganese variety is known as thulite, and is used for ornamental objects or out cabochon. It occurs in Norway and in Piedmont, Italy.
Chapter XIXVI
GEM MATERIALS OF ORGANIC ORIGIN Pearls
PEARLS, though an animal product, are held in great esteem by jewellers and lovers of gems in all parts of the world. They were known to the ancients, and held the highest place among gems, since the beauty of the pearl is entirely due to nature. The Hindus ascribed its origin to God Vishnu. Pearls were also held in great esteem by the Persians, and were known even in 2300 B.C. In ancient times, pearls were also paid as tributes. Pearls were also considered as emblems of purity, beauty and nobility and also to have possessed medicinal effects.
Pearls are found in the shells of oysters and mussels. These animals withdraw calcium carbonate from the sea-water and use it for building their shells, which are com­posed of organic material conchiolin and calcium carbonate in its two crystalline forms calcite and aragonite. The outside of the shell is conchiolin and the inner portion is composed of two layers—the outer of these consist of calcite and conchiolin and the inner of aragonite and conchiolin. The inner layer furnishes mother of pearl, etc.
Origin of pearl.—When a grain of sand or any other foreign object enters the shell of a mollusc, irritation is caused, which results in the secretion about the offending particle or parasite, layer by layer and then the pearl is built up. The knowledge of this phenomenon by man has
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