M. HartwalPs Epiaminatwii of some Minerals. 39 



composition, the latter having its composition represented by the 

 following formula : — 



2. Manganesian Epidote or Pistadte. 



The mineral found at St Marcet in Piedmont, and known to 

 mineralogists under the name Manganesian Epidote, was refer- 

 red to the epidote genus, on account of its series of crystalliza- 

 tions. 



This mineralogical determination it was desirous to have 

 confirmed by chemical analysis; and, further, chemists were cu- 

 rious to know the particular state of oxidation of the manga- 

 nese and iron which it contains. The following is the analysis 

 of Hartwall : — 



Silica. 

 Alumina, 



Per Cent. Quantity of Oxygen. 

 0.4425 38.47 19-35 



2030 17-65 8.34 



Lime, ... - 0.2490 21.65 6.08 



Peroxide of Manganese, 0.1620 14.08 4.17 



Peroxide of Iron,' - 0.0760 6.60 2.02 



Magnesia, - - 0.0210 \^ 0.70 



100.27 

 I have inferred, says Hartwall, by the calculation of the result 

 of the analysis, that the manganese and iron occur in the mineral 

 in the state of peroxide. This is proved not only by the dimi- 

 nished quantity of the isomorphous alumina along with them, 

 but also by the reddish-brown colour of the mineral. Accord- 

 ing to these data, the formula is as follows : — 



Al 



CftM 



k^S 



Vc 



