F. R. Van Horn — Pisanite and Arsenopyrite. 47 



crystals. The only faces observed were m (110) and 5.(010). 

 ]STo terminal planes were developed and all faces were rough. 

 The single crystal on the left in fig. 7 measures about 5 cm wide, 

 10 cm long, and 4 cm thick. The other two are twins after z (232). 

 The central crystal is 5 cm wide, 8 cm long, and 6 cm thick. The 

 largest specimen is the twin on the right which is tabular and 

 measures 8 cm wide, 9 cm long, and 3-| cm thick. The writer has 



Fig. 7. 



Fig. 7. Large staurolite crystals (one-half natural size) from Copper- 

 hill, Tennessee. The one on the left is a single crystal, and the other two 

 are twins after z (232). 



never seen any staurolites in this country or Europe which 

 approach the size of these crystals. All crystals were either 

 single individuals, or twinned after 2(232). and none twinned 

 after x (032) were found. It may possibly be a matter of 

 interest to know that out of several hundred small staurolite 

 crystals found near Mineral Bluff, Fannin Co., Georgia, only 

 11 were found twinned after a? (032). The remainder were 

 about equally divided between single crystals and those twinned 

 after z (232). The large staurolites of the Ducktown district 

 are all altered to an irregular aggregate of chlorite, muscovite, 

 and garnet, with a little magnetite. In some places the crys- 

 tals were evidently formed after the schistose structure of the 

 surrounding rocks was developed. 



Geological- Mineral ogical Laboratory, 



Case School of Applied Science, August, 1913. 



