1 835.] and Porphyritic Greenstone Rocks. 449 



examples occur at Muldakajewsk, near Miask, in Ural, wliich 

 contains crystals of Uralite with a nucleus of augite. There 

 are other varieties which assume a fine lustre and colour by 

 polishing. These are distinguished from ve^'de antique by 

 the large crystals of labradorite, which they contain, and 

 by the colour of the base. The following are the the spe- 

 cific gravities of some augite porphyries : — 



Absolute 

 wt. in grs. Sp. gr. 



1. Augite porphyry from Nicolajewsk, 



near Miask, in Ural 464'47 - 3*002 



2. Uralite porphyry from Maldaka- 



jewsk, near Miask 681*23 - 3*100 



3. Uralite porphyry, from Cavellinski, 



near Miask 416*88 - 3*030 



4. Uralite porphyry, from Mostowaja, 



near Katharinenburg, in Ural . 369*54 - 2*993 



5. Labrador porphyry, resembling ver- 



de antique . : 373*06 - 2*923 



6. Labrador porphyry, from Tscharisch 331*76 - 2*878 

 From this it is obvious that the Labrador porphyry pos- 

 sesses a less density than augite porphyry, which is to be 

 expected, considering that labradorite is lighter than augite. 



Crystals of uralite were taken out of the basis of the au- 

 gite porphyry of Mustowaja, and the crystals and basis 

 weighed separately. 



The sp. gr. of the uralite was found to be 3*150; that of 

 the basis, 2*991. This result is, however, not quite satis- 

 factory, as it was not possible to separate the crystals com- 

 pletely from the basis, and the base, when broken in small 

 portions, still contained uralite. 



The augite porphyry of Muldakajewsk melts in a platinum 

 crucible, in a strong heat, into a blackish-green translucent 

 glass. In a charcoal crucible, the augite porphyry of Mota- 

 waja, Cavellinski, and Nicolajewsk, fuses into an opaque 

 mass of a yellowish-white, or grayish colour. At the lower 

 part iron is collected, containing copper- red titanium. In 

 fusing verde antique a similar deposit is observed, with tita- 

 nium inclosed. 



Augite porphyry is found among all the rocks which are 

 usually termed greenstone ; but, in particular it occurs in 



VOL. II. 2 G 



