80 ECONOMIC GEOLOGY OF SILVERTON QUADRANGLE, [bull. 182. 
associated with chalcopyrite and pyrite. It was at first supposed to 
be black oxide of copper, but upon closer investigation proves to be 
a copper sulphide, probably chalcocite. 
Bornite. — Sulphide of copper and iron (3Cu 2 S.Fe 2 S 8 ). Contains 
55.5 per cent of copper. Isometric. Commonly massive. Copper 
red or pinchbeck brown on frssh fracture, but soon becomes irides- 
cent from tarnish, whence the name "peacock ore." Hardness, 3. 
Brittle. Specific gravity, 4.9-5.4. 
This mineral, often highly argentiferous by the replacement of a 
portion of the copper by silver, was a very important constituent of 
the large ore bodies. formerly worked in the Red Mountain district. 
According to T. E. Schwarz, it was the "principal ore for large 
masses" 1 in the Yankee Girl. It formed large solid masses in the 
Guston mine, associated with barite, the crystals of the latter being 
often embedded in the bornite. It also occurred in the Genesee- 
Vanderbilt mine. It is usually intimately associated with chalcocite 
and chalcopyrite. With quartz it occurs in bunches in the Silver Link 
mine and also in the John J. Crooke, a prospect north of Hensen 
Creek, associated with chalcocite. 
Chalcopyrite (yellow copper). — Sulphide of copper and iron (Cu 2 S. 
Fe 2 S 3 ), corresponding to 34.5 percent of copper. Tetragonal, sphe- 
noidal. Commonly massive. Brass yellow. Hardness, 3.5-4. Brittle. 
Specific gravity, 4.1-4.3. 
This is a common ore mineral throughout the quadrangle, and is 
sometimes auriferous, as in the Sound Democrat, or argentiferous 
(carrying also a little gold), as in the Yankee Girl, Guston, National 
Belle, and other Red Mountain mines, and in the Guadaloupe mine 
on Abrams Mountain. It is very abundant in the Titusville mine, 
in the New York City lode of the Silver Lake mine, and in the Ham- 
let mine. Associated with pyrite, it forms the ore of the Henrietta 
mine, and with tetrahedrite much of the ore of the Tom Moore 
lode. It is always present in ores carrying galena, sphalerite, and 
pyrite, although the amount varies widely in different occurrences. 
In the Saratoga mine it occurs with pyrite and galena, replacing 
limestone. 
Galena. — Lead sulphide (PbS). Isometric. Rarely showing ex- 
ternal crystal form, but characterized by its perfect cubic cleavage. 
Lead gray. Hardness, 2.5. Specific gravity, 7.5. 
This very important ore mineral, which when pure contains 86.6 
per cent of lead, occurs in nearly every ore deposit in the quad- 
rangle, although in extremely varying amounts. In the lodes of 
the Silver Lake Basin and vicinity it occurs in coarsely crystalline 
masses, associated with quartz, sphalerite, chalcopyrite, pyrite, and 
sometimes barite and tetrahedrite. Such coarsely crystalline varie- 
ties carry in this region relatively low silver values. In other lodes, 
1 Personal letter. 
