176 PHYSIOGRAPHY. CLASS II. 



Simple forms. P OD ; - = 139 IT ; P + oo 



(M) =103 42'; ?^ (p) = 61 49'; 



Pr 4 oo (s). 



Char, of Comb. Hemi-prismatic. 

 Combinations. 1. P oo. P 4- oo. Pr -f oo. 



Chessy. 



2. ?!. P OD. Pr + oo. Chessy. 



rfV 



3. P op. . P -f oo. Pr -f a?. Chessy. 



52 



Cleavage. Highly perfect in the direction of 

 and of Pr 4 OD, the former, however, 



still more easily obtained. Fracture conchoidal, 



uneven, scarcely observable in crystallised va- 



p 

 rieties. Surface, P oo rough ; -curved; 



Pr 4 GO sometimes vertically streaked. The 



rest of the faces smooth. 

 Lustre adamantine, inclining to vitreous. Colour 



grass-green, emerald-green, verdigris-green. 



Streak green, rather paler than the colour. 



Translucent, sometimes only on the edges. 

 Brittle. Hardness = 3-5 ... 4-0. Sp. Gr. = 4-008 



a cleavable variety from Chessy. 



Com/pound Varieties. Twin crystals : axis of 

 revolution perpendicular, face of composition paral- 

 lel to Pr 4 oo. Fig. 78. This composition occurs 



