384 Decomposition of Iron Pyrites. 



markings, lustre, and volume of the original substance (some- 

 times with a core yet unaltered), and with a brownish-red or 

 liver-color, whence such pseudomorphs have been called hepatic. 

 In regard to these, H. Bauerman 37 points out : " Here the 

 proportion of the unaltered constituent, iron (46.7 per cent.), 

 in the molecule of pyrites, is to that in the molecule of limonite 

 (60 per cent.) as 1 to 1.3, while their specific gravities are in 

 the inverse ratio of 1.4 to 1, or 5.0 for iron pyrites and 3.6 for 

 limonite." 



Where such crystals are enclosed in a rocky matrix, it has 

 been suggested that galvanic or electro-chemical currents have 

 been set in action by the introduction of moisture, through 

 which the crystals of pyrite have been attacked from the out- 

 side, free sulphuric acid released, and a decomposition of the 

 surrounding rock produced, sometimes with disintegration, or, 

 in other cases, it may be, with consolidation, e. g., by the pro- 

 duction of gypsum. 



A few instances of these pseudomorphs maybe here presented 

 from the works of Blum, 38 Both, 39 etc., and from my own col- 

 lection. 



Limonite after pyrite : 



Cubes, in Dutchess County, N. Y.; Yancey County, N. C. ; 

 Maryland, etc. 



Octahedra, in New Jersey ; in Llano and Bastrop counties, 

 Texas, etc. 



Gothite after pyrite : 



In Saxony; at Beresowsk, Siberia; in Maryland; at Monte- 

 video, etc. 



Limonite and gothite, one enveloping the other or the reverse, 

 after pyrite, or similar envelopments of limonite and compact 

 red hematite, after pyrite, at numerous localities : 



Striated cubes, sometimes six inches in diameter, in Switzer- 



37 Text-book of Syst. Min. (1881), 352. 



38 Pseud, rain. Reichs (1843), 187—197 ; Nachtrag (1847), 107, and (1863), 

 184, 185. 



39 Allg. u. chem. Geol. (1879), I, 102—105. 



