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Cornwall, Devonshire and Durham in England. In India it is found in Kishengarh State, Rajputana; Degana, Jodhpur State; Tavoy, Burma, and in small quantities in several other places.
, 14. Gypsum.—Satinspar is used in cheap jewellery, being a fibrous chatoyant variety with a silky lustre. It is cut cabochon as beeds, found in England and Russia. Hardness =2. Specific gravity =. It is usually
colourless, white, grey, yellow, brown, etc. Mean refractive index = Double refraction = Composition:
15.    Iolite.—It is also known as cordierite or dichroite, due to its pleochroism. Orthorhombic. It is a complex alumino-silicate of magnesium and iron. Colour: deep blue—not much used as a gem. Hardness = 7 to Specific gravity = Refractive index — It is found in Ceylon and is known as 'water sapphire'. It has been found in Travancore, in Trichinopoly and Madras, and in gem gravels in Mogok, Burma.
16.    Phenacite.—Good crystals are -obtained from the emerald mines of the Urals. It has a little fire and is little used as a gem. Hexagonal. Hardness =to 8. Specific gravity tm Colourless, yellowish or pale rose-red, transparent to translucent. Mean refractive index = 1-66, and double refraction =. Composition: It is obtained in the Mogok Ruby Mines of Burma. It somewhat resembles diamond but is lacking in fire. It is also obtained in the Ural Mountains, Brazil, Mexico and Colorado.
17.    Prehnite.—It is sometimes used as a gem, when it has an oily lustre and is found in rounded masses. Hard­ness = 6 to Specific gravity =. Colourless, white, light-green, apple-green, etc. Transparent to translucent. It occurs in France, Lake Superior, etc.
18.    Rhodonite.—It is a pink-red mineral, polishing well. It is used in Russia as an ornamental stone. It is
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