344 



M. A. Delesse's Researches on 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 mineral generally smaller than those of the porphyritic 

 granite, contains no feldspathic paste. Its essential charac- 

 ter is to contain 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 be- 

 fore 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 disseminated. 



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

 schistose varieties, hornblende, graphite, fibrolite. Some mi- 

 nerals of subsequent origin are common to the two granites, 

 as chlorite, 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 ave- 

 rage composition may be computed from the accompanying 

 table : for each analysis a large mass of the stone was re- 

 duced to powder, and the assay taken from this. 





SiO 3 . 



Al 2 3 . 



Fe 2 3 . 



MnO. 



CaO. 



Mgo. 



KO. 



NaO. 



Loss by 

 burning. 



Sum. 



I. 



II. 

 III. 



IV. 



76-3 

 75-4 



73-8 

 73-3 



12-8 



1-5 



trace 



0-8 

 0-6 

 0-9 



0-7 



trace 

 0-9 



...* 





080 



10000 



12-7 

 158 



7-8 



10'i 



1-6 







V. 



VI. 



72-0 

 70-4 



15-33 



0-4 



trace 



0-98 

 0-6 



0-60 



7-70 



2-00 



0-40 



99-50 



16-6 



VII. 



70-0 



17*3 





0-6 







... 



... 





VIII. 



67-3 



162 





1-9 



0-6 



... 









IX. 



66-7 



... | 1-8 





0-9 







... 







* The dots shew that the quantitative determination was not made. 



