1835.] Porphyritic Greenstone Rocks, 111 



boldt, Deppe, Meyen, and Sellow, from St. Felipe, in the 

 province of Jean de Bracamoros ; from Cuesta Grande de 

 Misantha, in Mexico ; from the crest of Monte Impossible, 

 province of St. Fernando, in Chili ; from the neighbourhood 

 of Gabriel Maxado, and Serpe, in Monte Video. The 

 splendid dioritic porphyry of Humboldt's collection from 

 Pisoje, near Popayan, is characterized by the large size and 

 beauty of the crystals of albite, and the smallness of the 

 hornblende crystals. Dioritic porphyry, with a gray basis, 

 large white albite, and small black crystals of hornblende, 

 (granito amandola) is found in Italy, and at Verospatak, 

 in Siebenbiirgen, forming the rock in which the gold mine 

 is worked. The albite is somewhat earthy; the rock con- 

 tains dodecahedral quartz of a large size, rounded on the 

 edges. 



The dioritic porphyry of Schemnitz, in which the silver 

 mine is worked, is similar. As accidental constituents, 

 green talc is met with in regular six-sided tables, and iron 

 pyrites ; it is mixed with fine calcareous spar, and effer- 

 vesces with acids, in all parts, as Beudant pointed out. 



3. Hypersthene Rock, — a granular mixture of labradorite 

 and hypersthene. 



The grains of labradorite have two cleavages, which cut 

 each other at the same angle, as in albite. The same com- 

 binations also occur among them, especially in the large 

 granular varieties of hypersthene rock, (as at Paul's Island, 

 coast of Labrador), where the variegated appearance upon 

 the perfect cleavage faces is a common occurrence. In 

 these large granular varieties it is grayish-white, very trans- 

 lucent, and mostly of the well known variety of colour which 

 appears on the second face of cleavage (M.) In the smaller, 

 large granular varieties, it is snow-white, strongly translu- 

 cent on the edges, and without the variety of colouring. 

 The faces of cleavage are, in this case, imperfect ; the frac- 

 ture small splintery. In these varieties it is difficult to 

 distinguish it from similar crystals of albite ; its capacity 

 of melting i)efore the blow-pipe is equally small ; it does 

 not change the colour of nickel and borax when it is 

 fused with these substances before the blow-pipe. Its sp. 

 gr. is higher, being to albite as 27 to 26. Yet, in the finely 

 granular varieties of hypersthene rock, this is difficult to 



