SILICATES, TITANATES, 1 



jr,7 



as is" indicated by the ni-ntrant angle. Particularly fine speci- 

 mens of thi> habit occur in a chloritic schist, associated with adu- 

 laria, apatite, titanitc, and calcite, in the Sulzbachthal, Tyrol. A 

 tabular habit, though not as common as the elongated habit, 

 also occurs, good specimens of which are obtained on the Prince of 

 \Val-s Island. Alaska; these are also twinned, the twinning being 

 revealed by the st nations on the clinopinacoidal face. Massive 



Fia. 494. Epidote. Sulzbachthal, Tyrol. 



and granular epidote mixed with quartz occurs as the rock epido- 

 site; it is derived from the alteration of plagioclase feldspars 

 together with some ferromagne'sian mineral, as pyroxene or amphi- 

 bole. 



Piedmontite is a brown or red epidote in which the iron is re- 

 placed by manganese ; it occurs in Piedmont, Italy, and also in a 

 rhyolite at South Mountain, Pennsylvania. 



In rock sections epidote appears colorless, pale yellow, or brown, 

 depending upon the percentage of iron; in tabular or elongated 

 crystals, at times intergrown with zoisite. The relief is high, and 

 the basal cleavage cracks are distinct. Pleochroism is strong in the 

 colored varieties, and much less in the colorless, or those poor in 

 iron. Interference colors are high, as the double refraction may 

 vary from .03 to .06. The extinction is inclined and varies from 2 



