^6 Gustav Rose on Greenstone and [Oct. 



The hornblende is grayish-black, and has a very perfect 

 and splendent cleavage. The crystals are long pillars, often 

 of considerable thickness, more or less strongly united with 

 the basis. They separate completely from it, and leave 

 their impression on the surface of its fracture, from which 

 their form can be determined. Before the blow-pipe small 

 portions fuse upon charcoal, with great frothing, into a 

 black bead, which, when not too large, is attracted by the 

 magnet. 



Similar accidental constituents are met with, asindiorite, 

 viz. quartz, mica, iron pyrites, and magnetic iron ore. Of 

 these the quartz occurs most frequently, and, in many 

 instances, in considerable quantity. It is then crystallized 

 in hexagonal dodecahedrons, with rounded edges, grayish- 

 white, transparent, and a fatty, splendent lustre. 



Albite and hornblende are frequently found enclosed in 

 equal quantities in the basis, and then, generally in such a 

 quantity, that the crystals occupy nearly as much space as 

 the basis. In other varieties the albite or hornblende dis- 

 appear. Where the albite is present, in small quantity, it 

 is commonly indistinct. 



The sp. gr. of a piece of dioritic porphyry, weighing 

 32*5866 grms. (501-8 grs.), from Pitatelewsky, near Bogos- 

 lowsk, where the gold is washed, containing perfect horn- 

 blende and indistinct crystals of albite, was 2*884. 



This porphyry melted in a charcoal crucible into a gray 

 glass, at the bottom of which iron regulus was formed, 

 containing, interspersed through it, some titanium, of a 

 copper-red colour. 



Dioritic porphyry occurs in Ural, frequently containing 

 albite and hornblende in nearly equal proportions, at the 

 foot of Auschkuls, at the Berkutskaya Gora, near Miask, 

 and at the gold washing station of Pitatelewsky, at Bogos- 

 lowsk ; at the last place, with much dodecahedral quartz ; 

 with distinct hornblende and subordinate albite, at Polo- 

 kowsky, near Miask, in the Frolowschen copper mine at 

 Bogoslowsk, and especially at the gold washing station of 

 Pitatelewsky; with albite, free from hornblende, in the 

 neighbourhood of Nischne Turinsk. Many American dio- 

 ritic porphyries, corresponding with those of Pitatelewsky 

 and the Frolowschen mine, exist in the collections of Hum- 



