THE 



AMERICAN JOURNAL OF SCIENCE 



[THIRD SERIES.] 



Akt. A 7 II. — On the Chemical Composition of Staurolite, and 

 the regular arrangemen t of its Carbonaceous Inclusions ; 

 by S. L. Penfield and J. H. Peatt. 



Historical. — In the early analyses of staurolite, especially 

 those of Jacobson* and Rammelsberg,f a great variation was 

 found in the chemical composition, especially in the amounts 

 of silica, which varied all the way from 27 to 50 per cent. 

 The iron oxide, moreover, was regarded by some investigators 

 as ferric, by others as ferrous, while still others considered 

 that it existed in both states of oxidation. 



In 1865 Lechartier^: observed that pulverized staurolite from 

 "Brittany and Bolivia, when examined with the microscope, 

 showed both brown and colorless grains. On treatment with 

 hydrofluoric acid, it was found that the colorless ones dis- 

 solved, while the staurolite was very slightly attacked. Fur- 

 thermore, material purified by this treatment was found to be 

 nearly uniform in specific gravity and gave amounts of SiO„ 

 varying from 28-29 per cent, agreeing with the purest stauro- 

 lite from St. Gothard. He also proved that water was an 

 essential constituent of the mineral. 



In 1872, von Lasaulx§ showed, from a microscopic examina- 

 tion of staurolite from various localities, that all crystals are 

 more or less impure from mechanical admixtures, especially of 



*Pogg. Ann., lxii, p. 419, 1844 and lxviii, p. 414, 1846. 

 f Pogg. Ann., cxiii, p.. 599, 1861. 

 ^Bull Soc. Cberaique, iii, p. 378. 

 §Min. Mittheilung, 1872, p. 173. 



Am. Jour. Sci.— Third Series, Vol. XLVir, No. 278.— Feb., 1894. 

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