ORDER vi. PRISMATIC AZURE-SPAR. 9QI 



the latter, P is an acute pyramid. Lateral edge 

 = 136 20'.* 



Cleavage, P -f- oo indistinct. Fracture uneven, 

 Surface smooth, all the faces alike. 



Lustre vitreous. Colour various shades of a pure 

 blue colour, particularly deep and beautiful, if 

 viewed in the direction of one line, apparently 

 the axis of the crystals, while perpendicular to it, 

 it is of a pale greenish-blue colour. Streak white. 

 Translucent, generally only on the edges, opake. 



Brittle. Hardness = 5-0... 5-5. Sp. Gr. = 3-056. 



Compound Varieties. Massive : composition gra- 

 nular, individuals strongly connected. 



OBSERVATIONS. 



1. According to FUCHS, the prismatic Azure-spar from 

 the Radelgraben in Salzburg consists of 



Phosphoric Acid 41-81. 



Alumina 3573. 



Magnesia 9-34. 



Silica 2-10. 



Protoxide of Iron 2'64. 



Water 6-06. 



Before the blowpipe it intumesces a little, and assumes a 

 glassy appearance, where the heat has been highest, but 

 does not melt. With borax it yields a clear colourless glo- 

 bule. Treated with boracic acid, and a piece of iron-wire, 

 it gives a globule of phosphuret of iron. 



2. It has been found in narrow veins, traversing clay, 

 slate, both massive and crystallised, with rhombohedral 



" The angles are given according to BROOKE and PHIL- 

 UPS. H. 



