48 ON PYRITE AND MA'RCASITE. [bull. 186. 
10. Chalcopyrite may bo sharply distinguished from chalcocite or 
bornite in pyrite carrying 3 per cent copper or less. A method is given 
for detecting small amounts of chalcopyrite in pyrite and mareasite, 
or the reverse, or in rocks. 
11. There is no evidence as to the state of combination or valency 
of iron in pyrite and mareasite, or that these diifer in the two minerals. 
Experiments which have been regarded as proving the existence of 
such differences are inconclusive. 
12. The principle of the oxidation method, with appropriate modifi- 
cations, is probably capable of wider application in distinguishing 
dimorphous minerals, in determining whether a given complex mineral 
is a mixture or compound of its simpler constituents, and in determin- 
ing the nature of small amounts of impurities. 
13. The action of acid permanganate on pyrite and mareasite is anal- 
ogous to that of ferric salts, the percentage of sulphur oxidized in 
pyrite being higher than in mareasite. 
My thanks are due to Dr. A. A. Julien, whose valuable assistance 
has been noted above, and to Professors Van Hise, Emerson, Merrill, 
and Penfield, and Messrs. Tassin, Emmons, Ransome, Weed, and 
Lindgren, who have generously supplied most of the material upon 
which the foregoing investigation is based. 
