SI l.K 'ATliS, TITANATKS, KTC. 



\'I. Uvarovito: Calcium ehrome garnet, CasCr 2 (Si0 4 ) ; CaO = 

 t 'r 2 O 8 = 32.50, SK) 2 = 38.23 ; H. = 7 ; G. = 3.4 ; Color, 

 bright green. Fuses with difficulty and will not gelatinize after 

 fusion. Tliis garnet is usually associated with chromite and with 

 serpentine; at ( >\ford, Canada, however, it is found in the cavities 

 of a granular limestone. It occurs at Wood's chrome mine, Lan- 

 ca-ter, Pennsylvania; at New Idria, California. 



In rock sections garnet appears in crystalline outline, granular 

 or irregular, colorless or in pale colors, with a high relief and a 

 rough surface and parting at times distinct. A zonal structure 



FIG. 485. Section of Garnet, showing the High Relief and Parting. 



is often noticed, especially in the titaniferous varieties. Isotropic, 

 but may exhibit anomalous weak double refraction, which is very 

 often a characteristic of the garnets of contact zones. 



Occurrence. Garnets occur as accessory minerals in rocks of 

 all varieties, the kind depending upon the nature of the magma. 

 Andradite and almandite are found in granites; pyrope is con- 

 nected with peridotites and serpentine; spessartite is found in 

 quartzite and rhyolite; grossularite is the common garnet of crys- 

 talline limestone; while all may be found in crystalline schists and 

 gneisses, as well as in metamorphic and contact zones. Eclogite 

 is a rock composed almost entirely of massive garnet. 



Garnet is easily decomposed by weathering, and forms chlorite, 

 iron ores, calcite, kaolinite, epidote, and a large number of second- 

 ary minerals, depending upon the chemical composition of the 

 original garnet. Garnets when fused break down, and the melt 

 on cooling forms other silicates, as anorthite, pyroxenes, or scapo- 

 lite. They are therefore unstable at the temperature of fusion. 

 Some garnets have been formed, as spessartite, by a simple fusion 



