Decomj)ontion of Iron Pyrites. 



177 



MARCASITE.— 6Vv/<^//i«6;f/. 



No. 



23 



Locality. 



6 



I 



lO 



"£ \ 



o 



H . 



iO 



W «2 



'"' 



-< s 



H 



H *< 



< 



» 



i P^ 



S^ 



1 ^ 



2 !^ 



1 



W ^ 



Ah 



> 



! C/^ 



•^ 







Supposed 

 Constitution. 



Sod 



Galena. 111. 



4 807 ' 2.315 I 96.53 

 97.50 



26 Hazelgreen, Wis. 4.805 2.797 



27 CrowBranch Mine, 4.720 0.996 

 . Wis. j 



28 Crow Branch Mine, 4.654 

 , I Wis. I 



30 Jefferson County, i 4.584 



N. Y. 



31 Schneeberg, Sax- 4.537 



ony. 



29 Jefferson County, 4.513 



N. Y. 



2.019 

 4.849 

 1.141 

 2.439 



S 1 



W : ! 

 HO I 



Ph 



3.48 

 j 2.50 



Tendency 



TO 



Decomposition. 



Tarnish and vitriol - 

 escence. 



Tarnish and vitriol- 

 escenee. 



1. Density of normal warcasite. In discussing these figures 

 it is desirable, first, to deduce the probable density of pure nor- 

 mal marcasite. On account of the visible admixture of quartz 

 and other impurities, the last five specimens, Nos. 27 to 31, 

 must be eliminated. In the remainder there is evident a halt- 

 ing of tlie figures near three points. 4.94, 4.88, and 4.86, but 

 still a marked progression from 4.805 to 4.987, with a corres- 

 ponding increase in hardness, lustre and resistance to oxidation. 

 All the fjicts seem to indicate that the density is increased by ad- 

 mixture with the heavier mineral, pyrite, and that the average 

 figure for marcasite, 4.9, adopted by Rammelsberg* as well as 

 the other, 4,847. deduced* from all the figures hitherto obtained 

 by other observers, are both too high from this cause. The 

 true specific gravity of normal marcasite may be therefore taken 

 as very near the figure 4.80. 



2. Latent conditution of marcasite crystals. If then we 

 may consider all these samples of marcasite as intimate inter- 

 mixtures with varying amounts of pyrite, without change of vol- 

 ume, the percentage proportions of the two minerals may be 



' Zeits. d. geol. Ges., (1864), XVI, 267. 

 2 This paper, Part I, 390 



