GUIDE TO THE MIXEKALOGIC COLLECTIONS 



95 



aiid potassium to some extent. As in the case of the pyroxenes 

 the varieties are divided into nonaluminous and aluminous. 



Amphibole occurs in monoelinic crystals of prismatic habit, 

 usually with an acute rhombic section and striated vertically ; a 

 typical section is shown in fig-. 211. Some of the common types 



Amphibole 



are given in fig. 212, 213. Columnar and fibrous masses are com- 

 mon, often radiated; also coarse or fine granular masses. The 

 luster is vitreous to pearly and often silky. The color varies 

 with different varieties but is mainly white, shades of green, 

 brown or black. 



VARIETIES 



Tremolite CaMg., (Si0.,) 4 . White or dark gray in color, some- 

 times transparent and colorless. Luster silky. 



Actinolite Ca(MgFe) 3 SiOJ 4 . Bright green to grayish green 

 in color. 



Nephrite (jade). A compact tough variety similar to the 

 jadeite described under pyroxene. 



Asbestos. A fine fibrous material white, gray, or greenish in 

 color, easily separated into threadlike fibers. 



Hornblende. An aluminous variety. Green, grayish green or 

 black in color. 



Amphibole occurs in crystalline limestone and in granitoid 

 and schistose rocks. It is an important constituent of many 

 granites, syenites and diorites. Good specimens have been 

 obtained in Orange, St Lawrence and Lewis counties, X. Y. 



Amphibole asbestos, which must not be confounded with the 

 fibrous serpentine passing commercially under the same name, 



