284 PHYSIOGRAPHY. CLASS II. 



Viewed in a direction parallel to the axis, the 

 colour of the crystals contains less yellow than in 

 the directions perpendicular to it. 

 Brittle. Hardness = 6-0... 7'0. Sp. Gr. = 3-269, 

 Zoisite from the Saualpe ; = 3-425, Pistazite 

 from Arendal. 



Compound Varieties. Twin-crystals : face of 

 composition parallel, axis of revolution perpendi- 

 cular to . This composition is very frequent, 



particularly among the varieties from Dauphiny. 

 Several varieties consist of concentric coats, the 

 outer ones of which being pealed off, leave a crystal 

 with smooth faces. Massive : composition granu- 

 lar, of various sizes of individuals, sometimes im- 

 palpable, strongly connected : columnar, straight, 

 and either parallel or divergent or irregular, and 

 of various sizes of individuals. 



OBSERVATIONS. 



1. The two species, Pistazite and Zoisite, comprehend- 

 ed within the varieties of prisraatoidal Augite-spar, are 

 easily distinguished by their colours. The colours of the 

 first are green, those of the second are white and grey, 

 but there are transitions in the colours of both. The 

 varieties of the present species, though less comprehen- 

 sive than the two preceding ones, form a series, the mem- 

 bers of which are analogous to the varieties of these spe- 

 cies. Thus Pistazite corresponds to the varieties called 

 Augite, Sahlite, Hornblende, and Actinolite, while Zoisite 

 answers to Diopside and Tremolite. This comparison ex- 

 tends even to the fourth species or prismatic Augite-spar, 

 whose varieties correspond to those called Diopside, Tre 



