SILICON. 179 



which the nepheline is mixed, (hornblende, meio- 

 iiite, &c.) introduce a slight excess of alumina, 

 or soda, by destroying the rigid purity of the 

 mineral. 



4. HEDENBERGITE, OR TR1SILICATE OF IRON. 



This mineral occurs in Marmor's mine, Tuna- 

 berg, Sweden, where it forms layers in white cal- 

 careous spar. It was described and analyzed by 

 M. Hedenberg, in the year 1807.* It has a 

 blackish green colour, a fibrous fracture, and it 

 seems to consist of rhombs, having the same fi- 

 gure as calcareous spar ; phosphoresces both by 

 heat and friction ; specific gravity, 3-154. The 

 constituents assigned by Hedenberg, but correct- 

 ed by Berzelius, are 



Silica . . . 40-62 



Protoxide of iron . 32-53 



Water . . . 16-05 



Carbonate of lime . 4-p3 



Oxide of Manganese . 0-?5 



Alumina . . . 0-37 



95-25t 



The carbonate of lime may be left out of view, 

 because it is obviously derived from the rock in 

 which the hedenbergite was found. 



* Afhandlingar, II. 164. f Nouveau Systems, p. 31. 



M2 



