PHYSIOGRAPHY. 



Staurotide. 



207 



Compound Varieties. Twin-crystals. Face of com- 

 position parallel, axis of revolution perpendicular to the 

 longer diagonal of the prism. Angle of revolution =90; 

 fig. 418. Face of composition parallel, and axis of rev- 

 olution perpendicular to a face replacing the terminal edg- 

 es, angle of revolution = 60, fig. 419. The individuals 

 in both cases, are continued beyond the face of composi- 

 tion, and produce cruciform groupes. By the addition of 

 a third individual to the latter, groupes resembling stars with 

 six radii, are formed. 



Fig. 418. Fig. 419. 



1. Before the blow-pipe this species does not fuse, but only assumes a 

 dark color. 



2. Analysis. 

 By VAUQUELIN. By KLAPROTH. 



from Brittany. from St. Gothard. 



3300 . . . 37-50 



44-00 . . 41-00 



Silica 



Alumina 



Lime . . 3-84 



Magnesia . . 0-00 



Oxide of iron . . 13-00 



Oxide of manganese 1-00 



000 



0-50 



18-25 



0-50 



3. It occurs in imbedded crystals in primitive rocks, particularly in 

 mica-slate, in simple and compound crystals, accompanied by Kyanite, 

 Garnet, &c. 



4. Simple crystals occur on St. Gothard in Switzerland, and the Grein- 

 er Mountain in Zillerthal in the Tyrol, sometimes curiously aggregated 



