54 NEW IORK STATE MUSEUM 



Chalcocite (copper glance) Cu 2 S 



Chalcocite is a copper sulfld containing 20.2$ sulfur and 79.8$ 

 copper. 



Though often occurring in orthorhonibic crystals (pi. 14 2 ) chal- 

 cocite is more frequently met with in masses which somewhat 

 resemble argentite but are much more brittle; it may be dis- 

 tinguished from bornite by the absence of the characteristic red- 

 brown color peculiar to bornite. The luster is metallic and the 

 streak and color lead-gray, the latter taking a dull black tarnish 

 on exposure. 



Chalcocite occurs coininonly associated with other copper 

 minerals. Beautiful specimens of this mineral are found in the 

 Cornwall mines. It occurs also in Bohemia, Saxony, Mexico and 

 South America. Interesting crystals are found at Bristol Ct., 

 and massive varieties to considerable extent at Butte Mont. 



Chalcocite is an ore of copper. 



Sphalerite (zinc blende or blende) ZnS 



The zinc sulfid known as sphalerite or blende contains 33$ 

 sulfur and 67$ zinc. 



Sphalerite often contains cadmium manganese and iron in 

 small quantities. It crystallizes in the tetrahedral group of the 



Fig. 164 Fig. 165 



Sphalerite 



isometric system (fig. 164, 165). In specimens from some locali- 

 ties the modification of the dodecahedron shown in fig. 165 has a 

 tendency by reason of repeated twinning to form a somewhat 

 curved face as in the specimen shown in pi. 15 ± . Massive 

 varieties are very common and show a perfect dodecahedral 

 cleavage. Compact masses of alternating layers of sphalerite 

 and galena also occur. The color ranges from black through red, 

 brown, yellow, green, to white, the more frequent shades being 



