Manchester Memoirs, Vol. xliv. (1900), No. 1. 



VII. The Formation of Minerals in Granite. 

 By C. E. Stromeyer, M.Inst. C.E. 



Received and read Jatiuary 2jrd, igoo. 



It is needless to recapitulate here the various sugges- 

 tions which have been \mt forward to account for the 

 curious fact that in granite we have an assemblage of 

 crystals so arranged as to leave no doubt that quartz, the 

 least fusible of the constituents, must often have been the 

 last to solidify. The differences between the melting 

 temperatures of quartz and felspars, micas and hornblendes 

 (as will be seen from Tabie I.), are as great as the difference 

 between the melting temperatures of ice and tin, lead or 

 zinc ; granite therefore presents to us a problem as difficult 

 to solve as if we were required to explain how water could 

 be made to freeze when in contact with, say, molten tin. 



Before trying to point out how this problem can be 

 solved, it will be as well to deal with two attempted expla- 

 nations. It has been urged that, given a molten mass of 

 granite which, if cooled under ordinary conditions, would 

 result in a solid resembling pitchstone, there would be no 

 tendency for the felspars, micas, &c., to separate from the 

 quartz. There are, however, numerous well-authenticated 

 facts to prove that this separation is possible under 

 certain circumstances. On heating to the right tempera- 

 ture an alloy of lead with a little silver, pure lead crystals 

 can be separated from the fluid lead-silver liquor. If salt 

 water is cooled to the right temperature below o"C., pure 

 ice is formed, while a more concentrated salt liquor 

 remains fluid. It is interesting to note that, although this 



May 4th, igoo. 



