70 PHYSIOGRAPHY. CLASS n. 



the first also in a dark violet blue variety from 

 St. Gallen in Stiria, the second in the yellow hexa- 

 hedral varieties from Saxony. Fracture con- 

 choidal, more or less perfect. 



Surface. The hexahedron generally smooth. Oc- 

 tahedron often rough and drusy. Dodecahedron 

 various, being sometimes smooth, at other times 

 rough or drusy. Hexahedral trigonal-icositetra- 

 hedrons commonly streaked parallel to their edges 

 of combination with the dodecahedron. Some- 

 times the faces of the hexahedron and the tetra- 

 conta-octahedrons are curved. 



Lustre vitreous. 



Colour white, though not very common, and seldom 

 pure. Generally wine -yellow or violet-blue. 

 Among its brightest colours are emerald- and 

 pistachio-green, sky-blue, rose-red, and crimson- 

 red. Very dark blue colours, bordering upon 

 black, probably owing to foreign admixtures. 

 Frequently different shades of colours are dis- 

 posed in coats parallel to the faces of the hexa- 

 hedron, or symmetrically distributed along the 

 edges or solid angles of crystals. 



Streak white. It is sometimes slightly tinged, if 

 the colours be very deep. 



Translucent ... transparent. Sometimes different 

 colours appear by reflected and by transmitted 

 light. 



Brittle. Hardness = 4-0. Sp. Gr. = 3-140, 

 violet-blue crystals from St. Gallen in Stiria, 



