308 



('. K. KEYES — EPIDOTE IX ERUPTIVE ROCKS. 



epidote fragments, which show a very close correspondence with epidote 

 of other Localities, particularly Ludwig's specimen from the Untersulz- 

 bach. The following are the results obtained from the Maryland speci- 

 mens by Dr Eillebrand, of the United States Geological Survey, and 

 from the Tyrolean locality by Ludwig. The Ti0 2 is probably due to the 

 presence of sph,ene, which was not separated from the powder completely : 



Epidote. 



■ Its Abundance in Maryland Granite. — The epidote of the allanite-bearing 

 granites of Maryland is frequently so abundant as to give a decided 

 greenish cast to the color of the rock. Under a pocket lens the yellowish- 

 green mineral is seen in small sharply hounded crystals or irregular 

 grains, showing glistening surfaces of fracture' and usually containing a 

 central reddish interior, which already has been shown to be allanite. 



Its microscopic Appearance — Under the microscope the epidote usually 

 appears in sharply denned crystals or grains enveloping reddish grains of 

 allanites, with which they are strictly isomorphous. Twins have not 

 been observed, though the included mineral is often twinned. The sec- 

 tions are transparent, colorless or slightly yellowish, with imperfect 

 cleavage. The pleochroism is quite marked, a being colorless or very 

 faint yellowish; t) light yellow, often tinged with green; r greenish 

 yellow. The absorption is r > ft > a. Interference colors brilliant. 

 The plane of the optic axe- is perpendicular to the cleavage and direction 

 of elongation. These characters, together with the chemical analysis 

 given, correspond in all particulars with those of rock-making epidote. 



Its Crystallography. — The simple crystals of epidote are usually quite 

 small, and commonly have their crystallographic planes much better 

 denned than in the other cases. The most frequently observed faces 



Si e ilso Bui. 64, U. S. Geol. Survey, p. 42. 



