12 
ON PYRITE AND MARCASITE. 
[BULL. 186. 
marcasite as pale bronze yellow. These discrepancies are doubtless 
due to tarnished specimens having been described. Marcasite 
frequently assumes a yellowish tarnish, which may vary to copper 
colored. On fresh surfaces, such as are obtained by breaking or by 
removing the film by warming with dilute hydrochloric acid, the color 
is unquestionably tin white or grayish white, closely matching 
platinum and without a trace of yellow. The white color is not an 
indication of the presence of arsenic, 1 as it is-equally shown b} 7 speci- 
mens which are free from arsenic. To distinguish pyrite and marcasite 
by the color, they must be cleaned with hydrochloric acid and imme- 
diately examined under a good white light, in comparison with 
standard specimens also freshly cleaned. The faint yellow of pyrite 
makes it extraordinarily easy to deceive oneself if the light be yel- 
lowish in tint. The differences of the supposed yellow and light- 
colored pyrites vanish, except in rare cases, when these precautions 
are observed, and pyrite can usually be distinguished with ease when 
mixed with marcasite. In the case of line-grained concretions, or 
where the surface is too rough to afford a good reflection, it is some- 
times quite impossible to draw any conclusion from the color. 
DENSITY. 
Density according to different authorities. — The density of both 
minerals is subject to some variation, as shown by the following 
figures from different sources: 
Density of marcasite and pyrite. 
Authority. 
Marcasite. 
Pyrite. 
Dana" . 
4.85-4.90 
4.90 
4.80 
4. 88-4. 90 
4.95-5.10 
Raminelsberg /> 
Julien c -.- _ . 
5.00 
5. 01 
Stokes d .. . 
5.02-5.04 
a System of Mineralogy, 6th ed., pp. 85, 94. 
b Zeitschr. Deutsch. geol. Gesell., Vol. XVI. 1864 , p. 267. Supposed normal density, 
c Annals New York Acad. S<-i. Vol. IV, 1887, pp. 177,210. Supposed normal density. 
dSee pp. 25,20. 
Density not a sure criterion of composition. — My own determina- 
tions were made with the pyenometer at 18°-23°, on the purest obtain- 
able material, coarsely powdered. Julien's figure for marcasite is 
certainly too low. The following list, giving the densities of some 
specimens of which 1 have determined the composition (after deduct- 
Op. cit., p. 95. 
