162 



Col- 

 lection 

 No. 



Locality 



Decomposition of Iron Pyritefi 

 ETCHED NUCLEI OF PYRITE. 



I 



Sp. 

 Gk. 



Etch- 

 ing 

 Agent. 



Characteristics of the 

 Etched Surface. 



31 French Creek, 

 i Penn. 



31 French Creek, 

 I Penn. 



39 Bristol, Conn. 



3 Marsden'sDlggings, 5.028 Br 

 111. 



6 Cochise Co., Ariz. 5.015 Br 



10 Gilpin Co., Col. ,5.011 Br 



10 Gilpin Co., Col. 5.011 NO'^ 



8 Alabama, N. Y. ! 5.011 ! NO'^ 



18 Doguatschka, Hun- 5.006 NO-' 

 I gary. I 



22 Central City, Col. 5.003 Br 



26 'French Creek, 5.001 Br 



I Penn. 



4.997 N0-= 



4.997 Br 



4.993 NO^ 



Man}' coarsely ciystalline irreg- 

 ular grains, projecting above 

 a tine matrix seamed up into 

 minute squares by the cubical 

 cleavage. 



Ver}' minutely and uniformly 

 mammillated to a shagreen- 

 like surface, cau.sed by pro- 

 jecting spherules and cubes. 



A similar shagreen-like surface, 

 but with a few projecting 

 coarse grains. Granules of 

 the groundmass mostly cubes 

 and square plates, in rounded 

 aggregations or spherules. 



The same, with the round or el- 

 liptical form of the spherules 

 and pits well marked : diam- 

 eter, 9.8 to 66.7 //', averaging 

 about 40 // (1-625 inch). Gran- 

 ules about 6 ii in diameter. 



Shagreen-like spherules, 17 to 82 

 fj. , averaging 44 i.i ; often rect- 

 angular, and commonly made 

 up of exceedingly minute 

 cubes. 



The same shagreen-like surface. 

 Granules less distinct and 

 regular, averaging 3.7// in di- 

 ameter. 



^linutely shagreen-like. Many 

 round pits. Also larger ellip- 

 tical grains projecting. Wid- 

 ened cracks abundant. 



Minutely shagreen-like, the com- 

 ponent cubes about 4 // in di- 

 ameter. Surface furrowed by 

 short branching lines. 



Much roughened by irregular 

 lines and clefts, with small 

 shagreen-like patches here and 

 there. 



Coarser grains (sometimes octa- 

 hedra) projecting above the 

 predominant, very fine grained 

 a:roundmass. 



Like No. 26. 



^ The standard ft or micra equals 0.001 millimeter, or about 1-25,000 of 

 an inch. 



