ORDER VI. PUISMATIC DYSTOME-SPAR. 



a : b : c : d = 33-8 : C7'17 : 53-95 : 1. 



Simple forms. P 00(6); -H ? j ^ } = 



(Pr) 5 ,.. (P) 5 , 



- (*) ; ~ ( 



43 56'; ftr+ oo (5); Pr (^ = 115 45'; 

 | Pr + 1 (r) = 93 26'; Pr + 1 (o) = 77 # ; 

 Pr + or> (w). 



Char, of Comb. Hemi-prismatic. Inclination of 

 P CD on f r + QD = 91 4V 30". 



Combinations. 1. P oo. -. . Pr+1.. 



P + oo. (**_+_?)!, ?r -f oo. Fig. 67. Arendal, 

 Norway. 



/ of the figures, and with his prism e l = 77 SCX in 

 Humboldtite, while the prisms a 1 = 115 3^ in Datolite, and 

 m = 115 45' in Humboldtite, also possess a similar situation, 

 that of d in the figures. The difference in the angles, particu- 

 larly the incidence of P cs on P + cs, giyen as 90 in Da- 

 tolite, and 91 41' 30" in Humboldtite, remain to distinguish 

 the crystals of the two bodies ; but a new comparison of them, 

 under this point of view, would yet be desirable. Their hemi- 

 prismatic character was first given in the Characteristic of the 

 Natural History System of MOHS, the angles, from want of 

 other measurements, were indicated upon the authority of 

 HAUY. Also the variety from America is decidedly hemi- 

 prismatic. H. 



VOL. 11. 



