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Ch. 20: Peridot

Ch. 19: Zircon Page of 187 Ch. 21: Quartz Text size:minus plus Restore normal size   Mail page  Print this page
     
     
 
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Zircon is recovered from the Travancore beach sands by the Travancore Minerals Co., Ltd., and is exported to U.K., Germany, U.S.A. and Austria for industrial purposes. The sands here contain 6% of zircon. It occurs only rarely in large amounts. The largest crystal on record weighed 15 lb. which is exceptional.
Chapter XX
OLIVINE OR PERIDOT
Introduction
IT is an important rock-forming mineral and is widely known. Olivine is known to the jewellers as 'peridote' and 'chrysolite'. The term olivine is also improperly used for green garnet and other green stones. It crystallizes in the orthorhombic system and may occur as crystals or grains. The cleavage is pinacoidal in two directions. Fracture is conchoidal. Specific gravity = 3-2 to 3-4 or even higher. Hardness = 6-1/2 to 7 (not high enough for a gem). Colour: Various shades of green, yellow, brown, reddish, etc. The best colour is a beautiful bottle green. Peridote is olive-green. Lustre: Vitreous to greasy; trans­parent to translucent. Olivine is biaxial and optically positive. Mean refractive index = 1-66 to 1-68. Double refraction = 0-04 (high). The dispersion is 0-018. Com­position: Mg2SiO4-Fe2Si04. Intermediate varieties are called olivine.
Uses
Peridote has a bottle green colour and is used for gems. Its hardness is 6, and being less than that of quartz, the mineral is subject to quick wear. Hence it is not suitable for rings. The stones are usually cut brilliant or step, hut the cabochon is sometimes used.
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Ch. 19: Zircon Page of 187 Ch. 21: Quartz
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