PHYSIOGRAPHY. CLASS 11. 



HAUY. Trait e, T. III. p. 391. Tabl. comp. p. 74. 

 Traite, 2de Ed. T. III. p. 258. 



Fundamental form. Scalene four-sided pyramid. 



Vol. I. Fig. 9. 



Simple forms. P 00(0); P 1 (z) ; P (y) ; 

 P + oo (M) = 120 (nearly) ; r ; Pr + 1 (P) ; 

 r -f QD (h). 



Char, of Comb. Prismatic. 

 Combinations. 1. P QD. P -f oo. ?r + oo. 



Andreasberg, Hartz. 

 & P oo. P 1. P. Pr-fl. P+oo. r-f oo. 



Fig. 28. 



Cleavage, P QD and fr distinct, the former 

 streaked parallel to the edges of combination with 

 Pr ; imperfect in the direction of P + oo. Frac- 

 ture uneven. Surface in general smooth. 

 Lustre metallic. Colour silver-white, inclining to 



tin-white. Streak unchanged. 

 Hardness rr 3-5. Sp. Gr. = 9*4406, HAUY ; 

 = 9-820, KLAPJIOTH. 



Compound Varieties. Twin-crystals : face of 

 composition parallel, axis of revolution perpen- 

 dicular to a face of P -f- oo. It is often repeated in 

 parallel layers, or in layers parallel to both the faces 

 of P + GO. The result is as in prismatic Lime- 

 haloide, di^prismatic Lead-baryte, and other species, 

 and similar therefore to Figs. 38. and 39. Mas- 

 sive : composition granular, individuals of various 

 sizes, and easily separated. Pseudomorphic six- 

 sided prisms. 



