34 ON PYRITE AND MARCASITE. [bull. 186. 
Cu), from which it may be concluded that pyrite or marcasite is pos- 
sibly an intermediate product of the oxidation of chalcopyrite" by 
ferric solutions. 
IX. FORM OF OCCURRENCE OF COPPER IN COPPER-BEARING 
PYRITES. 
The problem of determining whether a given specimen of cuprifer- 
ous pyrite contains its copper in the form of chalcopyrite or chalcocite 
was suggested by a geologist, and the following shows that such deter- 
mination is possible when marcasite or other sulphides are not present 
in considerable quantities. 
OXIDATION EXPERIMENTS. 
Mixtures of pyrite with chalcopyrite, chalcocite, and bornite were 
prepared, each containing 3 per cent copper. For chalcopyrite and 
chalcocite these mixtures have the following composition: 
Pyrite 91.331 ( Cu " 3 - 00 
Chalcopyrite 8.67? ° r ' Fe " " 45 ' 2U 
Pyrite . 96.24 
Chalcocite 3. 76 
S_ r - 51.80 
Cu 3.00 
Fe . 44.85 
S 52.15 
The bornite mixture has an intermediate composition. It would 
be scarcely possible to distinguish these by ordinary analytical 
methods, especially in the presence of small amounts of impurity. 
The values of p were found to be : 
Pyrite-chalcopyrite 62. 7 
Pyrite- chalcocite . . 75. 9 
Pyrite-bornite. ... : 76. 4 
It appears that the oxidation method does not admit of distinguish- 
ing chalcocite and bornite with certainty in a pyrite with 3 per cent 
copper, but that these may be readily distinguished from chalcopyrite 
even when the copper is considerably less than 3 per cent. It can 
also be determined with some probability whether a mixture of chal- 
copyrite with the other sulphides of copper is present. In the present 
case the figures given by chalcocite or bornite and chalcopyrite differ 
by more than thirteen times the probable error of a determination. 
This method will probably be of value in synthetic studies of cop- 
per ores. It is thus made possible, for example, to ascertain whether 
the first action of a cupric salt on pyrite is to produce chalcopyrite 
alone or a mixture of this with the other sulphides, without having 
to wait for the slow process of crystallization to produce the minerals 
in a form in which they can be recognized under the microscope. 13y 
