210 PHYSIOGRAPHY. CLASS II. 



Cleavage, parallel to the sides of a four-sided prism 

 of about 93, more perfectly parallel to the short 

 diagonal of that prism, traces parallel to the 

 long diagonal. Fracture uneven. 



Lustre eminent metallic-pearly upon the single per- 

 fect faces of cleavage ; in other directions more 

 or less distinctly vitreous. Colour greyish- or 

 greenish-black ; several varieties almost copper- 

 red upon the perfect face of cleavage. Streak 

 greenish-grey. Opake, in some varieties slightly 

 translucent on the edges. 



Brittle. Hardness = 6-0. Sp. Gr. = 3-389, the 

 American variety. 



Compound Varieties. Massive : composition 

 granular, sometimes of considerable size of indivi- 

 duals ; faces of composition uneven and rough. 



OBSERVATIONS. 



1. According to KLAPROTH, the prismatoidal Schiller- 

 spar consists of 



Silica 54-25. 



Magnesia 14-00. 



Alumina 2-25. 



Lime 1-50. 



Oxide of Iron 24-50. 



Water 1-00. 



and a trace of oxide of manganese. If heated alone, it is 

 little altered in appearance, but melts upon charcoal into a 

 greenish-grey opake globule, easily soluble in borax. 



2. The varieties of the present species occur engaged in 

 a mixture of Labradore, a species of the genus Feld- 

 spar, of hemi-prismatic and paratomous Augite-spar. The 

 rock often contains octahedral Iron-ore, and seems to be 



