1896.] NEW YORK ACADEMY OF SCIENCES. 27 



strictly correct, as the presence of cyanite inclusions and the 

 frequent intergrowths of this mineral render it almost impossi- 

 ble to procure pure material. The anal^yses also can be reduced 

 to terms of the molecules with favorable results by assuming 

 that all the alumina, except the small amount necessary to bind 

 the soda, to be present in the molecule AlaSiO,,. 



In order to test the matter, a further analysis of omphacite 

 was made by Dr. Locke, at the Mineralogical Institute of Heid- 

 elberg which yielded about 1 per cent, less alumina. Though 

 several analyses should be made before the question can be con- 

 sidered settled, yet this result would tend to show that some, 

 and perhaps not an inconsiderable part of the AljOg arises from 

 impurities. 



A constituent, which often accompanies the omphacite and 

 many times replaces it, is hornblende. The most common variety 

 has in thin section a light green to dark green color, and is 

 strongly pleochroic with various shades of green. The ab- 

 sorption is c > ir > tx. A dark variety has been identified by 

 Breithaupt and Sandberger as being Kaiinthin which is said to 

 contain about 12 per cent. AUOg. Its optical properties, how- 

 ever, agree with the common hornblende and as no analyses of 

 this occurence have been made, there ma\' be no ground for any 

 such distinction. 



In a few places, and especially near Eppenreuth, fibrous actin- 

 olite is the principle hornblendic mineral. 



The amount of hornblende present varies with that of pyrox- 

 ene, the3^ mutually replacing each other. Both hornblende-free 

 and omphacite-fi'ee eclogites occur. 



Cyanite is an important constituent in some of the rocks but 

 entirel}^ wanting in others. It seems to stand in close relation 

 with the pyroxene, generally accompan3dng this mineral, and 

 sometimes is present in quantities sufficient to giA'e a bluish 

 tint to the green ground-mass. It is as a rule idiomorphic and 

 forms rather stout crystals with twining on the macro-pinacoid. 

 Goniometric measurement on isolated individuals showed the 

 presence of a, M, c and x. 



Zoisite, characterized by its low interference colors and high 

 relief, is found in some of the hornblende eclogites and may 

 attain considerable importance in them. Fine crj'stals are 

 found on the Weissenstein near Stammbach where they occur in 

 pegmatite veins which cut through the eclogite. 



Rutile is constant in its association and appears as irregular 

 grains or as minute inclusions in the other minerals. In the 

 latter case it is well crystallized. It is often surrounded by a 

 light colored rim of titanoraorphite var^- ing from the most delicate 



