Quantcast
  Due to a new server, slow response may occur for which we apologize Portal logo
Login/Register
Bactrian Gold Treasure from Afghanistan, coming soon....
/gemstones/bahadur_handbook_of_precious_stones/page_155 - 2
 

Ch. 25: Other Semi-Precious Stones

Ch. 25: Other Semi-Precious Stones Page of 187 Ch. 25: Other Semi-Precious Stones Text size:minus plus Restore normal size   Mail page  Print this page
inferior hardness and optical properties. Hardness = Specific gravity = Lustre: Vitreous, dichroic, the
table should be cut parallel to the vertical axis. Refractive index:- Composition:
6.    Cassiterite.—Transparent cassiterite is rare, but is sometimes used as a gem. Good crystals occur in Cornwall, England, Germany and Bolivia.
7.    Chloroastrolite.—A greenish fibrous mineral with chatoyancy. Hardness = Specific gravity = The gem is cut cabochon and worn in pins, brooches, etc.
8.    Cyanite occurs in bladed triclinic crystals. Hardness (varies with direction) = 4 to 7. Specific gravity =to 3*7. The mineral is light to sky blue or white, grey, green, brown, etc. Colourless. Lustre: Vitreous, transparent to translucent. Refractive index =; and double refrac­tion = 0016. Composition: Clear cyanite with good colour may be cut for gems. It occurs in metamorphic rocks. Important localities: Switzerland, Tyrol, Brazil, etc.
9.    Diopside of a pleasing green colour is sometimes ob­tained. Hardness = 5 to 6. Specific gravity = Mean refractive index =; double refraction = Biaxial and optically negative. It occurs in metamorphosed limestones as an associate of diamond in the mines of South Africa. Good crystals are obtained at Piedmont, Italy, the Tyrol, Ontario and New York.
10.    Enstatite, Bronzite and Hypersthene.—These are isomorphous minerals with varying proportions of iron and magnesia. They are occasionally used for gem purposes. Bronzite has a chatoyant bronzy lustre and hypersthene has a metalloidal iridescent lustre, when cut cabochon. Orthorhombic pyroxenes—colour varies from greyish white, greenish, yellowish, etc. Hardness = 5. to 6. Specific gravity =. Mean refractive index =
11.—Euclase. It is a beryllium mineral which is obtained in the Urals and Brazil. It occurs as small monoclinic crystals with perfect cleavage in one direction.
156
Ch. 25: Other Semi-Precious Stones Page of 187 Ch. 25: Other Semi-Precious Stones
Suggested Illustrations
Other Chapters you may find useful
bullet Tag
This Page