Note on Copper Minerals. — A. N. WinchcU. 24$ 
O'Harra calciiier along the rails in the bed of the furnace. In 
fact, they not only form beneath the flanges of the rails, but 
also slowly replace the rails themselves. This replacement 
continues to such an extent that finally, when the rails are 
taken out, they have only a thin upper surface layer of iron ; 
all the rest has been transformed into chalcopyrite and born- 
ite, with the exception of that portion of the rails completely 
embedded in the brick bed of the furnace. Furthermore, the 
replacement is so gradual that it is impossible to distinguish 
any exact line of demarcation between the remaining iron of 
the rail and the mineral sulphides. 
An examination of these sulphides shows that, while they 
are somewhat impure from mechanically admixed quartz and 
perhaps some other foreign matter, they exhibit the true char- 
acters of chalcopyrite coated in places with films of bornite, 
occasionally of appreciable thickness. Thus, the former min- 
eral has an uneven fracture, a hardness less than 4, a brass 
vellow color, and a greenish streak. The specific gravity is 
considerablv decreased by foreign matter present, being only 
about 3.8. Ihe mineral occurs both finely and coarsely crys- 
talline, and these varieties pass abruptly into each other. In 
a small lenticular cavity several crystals were found, which at- 
tained only about one- fourth of a millimeter as a maximum 
diameter. They were nearly all tarnished by a coating of 
bornite, but a few retain a brass yellow color. They present 
the tetahedral aspect predominatingly ; some seem to be mere 
triangular tablets. Twinning occurs, apparently parallel to 
(hi), and striations are abundant. 
The massive mineral was subjected to partial analysis. The 
copper was determined by means of the potassium cyanide 
method, the iron being filtered ofif and weighed after the titra- 
tion was nearly completed. The powdered mineral was treated 
with boiling nitric acid for about half an hour, and it is there- 
fore possible that small amounts of silica and alumina are in- 
cluded in the iron percentages ; the sulphur was determined by 
the ordinary barium sulphate method. The analysis was car- 
ried out in the mineralogical laboratory of the Montana State 
School of Mines on material presented to the school by Mr. 
John Gillie, superintendent of tlie TUitte & Boston Consol- 
idated Mining Co. 
