122 



THE DAWN OP LIFE. 



resembles closely under the microscope the corralloidal forms 

 of arragonite known as fios ferri, the surfaces being somewhat 

 rugose and glistening with crystalline faces. This silicate is 

 sub-translucent, and of a pale green colour, but immediately 

 becomes of a light reddish brown when heated to redness in 

 the air, and gives off water when heated in a tube, without 

 however, changing its form. It is partially decomposed by 

 strong hydrochloric acid, yielding a considerable amount of 

 protosalt of iron. Strong hot sulphuric acid readily and com- 

 pletely decomposes it, showing it to be a silicate of alumina 

 and ferrous oxide, with some magnesia and alkalies, but with 

 no trace of lime. The separated silica, which remains after the 

 action of the acid, is readily dissolved by a dilute solution of 

 soda, leaving behind nothing but angular and partially rounded 

 grains of sand, chiefly of colourless vitreous quartz. An 

 analysis effected in the way just described on 1'187 grammes 

 gave the following results, which give, by calculation, the cen- 

 tesimal composition of the mineral : — 



1-1869 



100-00 



"A previous analysis of a portion of the mixture by fusion 

 with carbonate of soda gave, by calculation, I8'80 p. c. of pro- 

 toxide of iron, and amounts of alumina and combined silica 

 closely agreeing with those just given. 



" The oxygen ratios, as above calculated, are nearly as 3 : 2 : 

 1 : 1. This mineral approaches in composition to the jollyte of 

 Yon Kobell, from which it differs in containing a portion of 

 alkalies, and only one half as much water. In these respects 

 it agrees nearly with the silicate found by Robert Hoffman, at 

 Raspenau, in Bohemia, where it occurs in thin layers alterna- 



