36 <>N PYRITE AND MARCASITE. 
Quantitative composition of specimens of doubtful nature. 
[Figures in parenthesis were determined by the indirect method.] 
[BULL. 186. 
No. 
< >riginal designation, 
etc. 
Locality. 
p. 
Pyrite. 
Marcasite. 
Percent. Percent. 
15 
Concretion from 
Unknown . 
30.1 
63.0 , 37.0 
coal. 
16 
Pyritized ammo- 
nite. 
Folkestone, England. 
46.9 
88.0 
12.0 
17 
Fibrous marcasite. 
Red Cloud mine, 
Colorado. 
65.7 
100.0 
18 
Pyrite with mar- 
casite. 
Cjuartzburg district, 
Oregon. 
38.6 
78.0 
22.0 
19 
Marcasite 
Chautauqua tunnel. 
Idaho. 
51.3 
93.5 
6.5 
20 
_._do 
Garfield tunnel, 
Idaho. 
19.8 
30. 5 (34. 4) 
69. 5 (65. 6) 
21 
Marcasite nodules _ 
South Dakota 
60.3 
100.0 
22 
Marcasite (se- 
lected). 
Littmitz, Bohemia . _ . 
19.5 
29.5(27.8) 70.5(72.2) 
23 
do 
Crow Branch mine, 
Wisconsin. 
IS. 6 
26.0(31.0) 
74.0 (79.0) 
24 
Fibrous marcasite. 
Sunshine, Colo 
52. 2 
a 94.0 
7>6.0 
25 
Marcasite after 
pyrite. 
Folkestone. England 
55. 4 
97.0 
3.0 
26 
Pyrite ore 
Rio Tinto. Spain 
65.7 
10.0.0 
27 
Pyrite octahedra - . 
Unknown 
80.4 
100.0 
(c) 
Or more. 
h Or less. 
c Much cobalt. 
No. 15. Nearly spherical concretion from coal; locality unknown. Weight, 9.2 
grams. Very hard. The structure is coarsely fibrous and radial, with concen- 
tric shells of pyrite and marcasite, easy distinguishable by their color. 
No. 16. Pyritized ammonite from Folkestone. England. The walls of the cav- 
ities are incrusted with pyrite crystals, but the nature of the mass can not Le 
determined from the color. 
No. 17. Concretion from Red Cloud mine, San Juan County, Colo., supposed 
to be marcasite. It consists of a finely fibrous incrustation on rhyolite, varying 
in thickness from 1 to 10 millimeters, with mammillary surface, and with a banded 
structure and cleavage perpendicular to the fibers. The banded structure is due 
to tha inclosure of quarts and a black substance which, judging from the presence 
of a little copper, lead, and arsenic, may be galena, arsenopyrite, and chalcocite. 
The latter would account for the high oxidation coefficient, which could not be 
caused by the first two (pp. 32-33). Carefully selected material gave a specific 
gravity of 4.563. 
No. 18. The occurrence of this material is thus described by Mr. Lindgren, by 
whom it was submitted for a determination of the yellowish-gray material: 
