M. A. Delesse's Researches on Granite, 



209 



The large amount of silica is no doubt due to quartz mecha- 

 nically mixed. 



Orthose and quartz are found in the most degraded varieties 

 of this granite. 



The feldspar of the sixth system is rare, and only found in 

 the most crystalline varieties. 



The granite of the Vosges, although its grain is fine and its 

 minerals generally smaller than those of the porphyritic granite, 

 contains no feldspathic paste. Its essential character is to con- 

 tain two micas, the one dark the other bright. The first is 

 identical with the mica of the Ballons. The second is silver- 

 white or violet-gray ; its dominant base is potash ; it resists the 

 action of sulphuric and hydrochloric acids, and is altogether the 

 same as that I have described before as occurring in the veins of 

 pegmatite (Ann. des Mines, 4th ser. vol. xvi. p. 100). The clear 

 is less abundant than the dark mica, and is less uniformly dis- 

 seminated. 



The accidental minerals are garnet, pinite, and, in the schis- 

 tose varieties, hornblende, graphite, fibrolite. Some minerals 

 of subsequent origin are common to the two granites, as chlo- 

 rite, carbonate and oxides of iron, heavy spar, fluor spar, &c. 



The granite of the Vosges is very much fissured and cut up 

 by veins and lodes. Its density is about that of quartz, and is 

 less than that of the granite of the Ballons. Its average com- 

 position may be computed from the accompanying table : for 

 each analysis a large mass of the stone was reduced to powder, 

 and the assay taken from this. 



The dots show that the quantitative determination was not made. 



Phil. Mag. S. 4. Vol. 6. No. 38. Sept. 1853. P 



