446 Gustav Rose on Greenstove [Dec. 



the stone is fractured, the diallage appears to be present 

 in greatest quantity, although it is very thin. 



In Ural a peculiar kind of gabbro occurs. A very large 

 grained variety is found at Neurode in Silesia, consisting 

 of grayish-white translucent labradorite, and olive-green 

 diallage, also at Baste in the Hartz, and near the Village of 

 Prese in the Valteline. A very fine variety exists in the 

 American collection of Humboldt, from Ayavaca in Peru, 

 consisting of much greenish-gray diallage, and some 

 greenish-white translucent labradorite ; gabbro mixed with 

 serpentine is found at Florence and Brian^on. 



5. Augite porphyry consists of a basis with inclosed horn- 

 blende and crystals of augite. The basis has usually a dull 

 green and gray colour, like that of dioritic porphyry, but 

 is darker and more like basalt. Its hardness is about equal 

 to that of the basis of dioritic porphyry ; its fusibility is 

 smaller. It melts before the blow-pipe in the platinum 

 forceps, commonly on the edges into a blackish green glass; 

 muriatic acid when digested on it in a pulverized state 

 takes up alumina, oxide of iron, and much lime ; magnesia 

 and an alkali are probably also present. 



The crystals of labradorite are much like felspar, being re- 

 gular six-sided prisms which usually by the extension of the 

 faces, (M) corresponding with the second faces of cleavage 

 become so broad, that in the mass, they appear from their 

 transverse fracture to be thin stripes. They are, however, 

 like the combined pieces, twin crystals ; and the most perfect 

 face of cleavage, (P) of the apparently single crystal pos- 

 sesses the resulting angle described ; still the faces of 

 cleavage are rare, and are only seen in the crystals as pure 

 and translucent as the albite of dioritic porphyry. The 

 crystals are mostly, scarce translucent, and the fracture 

 indistinct and splintery. The colour is partly snow-white, 

 and partly by mixture with the basis greenish and grayish- 

 white. Their size varies ; the largest. Rose found in the 

 augite porphyry of Ajatskaja, 130 versts (86 miles) to the 

 north of Katharinenburg in Ural, where their length, with 

 a considerable breadth, is more than an inch ; frequently, 

 however, they are small. In this case, they protrude very 

 little out of the basis which is then light coloured, and 

 scarcely darker than the crystals of labradorite. The large 



