GUIDE TO THE MIXERALOGIC COLLECTIONS 



99 



VARIETIES 



1 Aluminium garnet. Grossularite Ca 3 Al 2 (Si0 4 ),. White, pale 

 yellow, pale green, reddish, brown or rose-red in color, rarely 

 emerald-green from the presence of chromium. 



Pyrope Mg.AL (Si 4 ) 3 . Deep red to nearly black in color. 

 Transparent specimens are cut for gems. 



Almandite Fe.AL (Si0 4 ) 3 . Deep red to black in color. This 

 variety includes many of the common garnets and when trans- 

 parent is cut for gems. 



Spessartite Mn 3 Al 2 (Si 4 ) 3 . Dark hyacinth-red, violet-red to 

 brownish red. 



2 Iron garnet. Andradite Ca 3 Fe 2 (Si 4 ) 3 . Various shades of 

 yellow, green, red, brown and black in color. This variety is 

 quite common. 



3 Chromium garnet. Uvarovite Ca 3 Cr 2 (Si0 4 ) 3 . In minute crys- 

 tals of an emerald-green color. 



Garnet, particularly the variety almandite, occurs abundantly 

 in gneiss and the crystalline schists. Grossularite is character- 

 istic of the contact zones of intruded igneous rock in the crystal- 

 line schists. Pyrope is found in many basic igneous rocks, and 

 spessartite in granite rocks, quartzites and whetstone schists, 

 also in rhyolite. Uvarovite is found with chromite in serpentine 

 and in granular limestone. Pink garnets embedded in marble 

 are found at Mordos Mex. In New York garnet is found in 

 Essex, Warren. Orange, Westchester and New York counties. 



Garnet is extensively used as abrasive material. The Mexican 

 marble mentioned above is polished for ornamental purposes 

 and transparent red and green varieties are cut for gems. 



Chrysolite (olivin, peridot) (Mg.Fe) 2 Si0 4 



Chrysolite is an orthosilicate of magnesium and iron. It rarely 

 occurs in urthorhombic crystals but is usually found in trans- 

 parent to translucent granular masses, disseminated grains or 

 as sand. The luster of chrysolite is vitreous and the color a 

 yellowish green, olive-green, or bottle-green to brownish red. 



Chrysolite occurs as an essentia] constituent of peridotite and 

 of some gabbros. It is found in eruptive rocks such as trap, 

 basalt, etc. and as a product of the metamorphism of certain 

 sedimentary rocks containing magnesia and silica. 



