ransome.] GANGUE MINEEALS. 71 
posed of interlocking grains with incomplete crystal boundaries (see 
PL IX, A and B). Distinct crystals are found only in small vugs 
and are never of large size. A radial arrangement of the imperfectly 
formed crystals was noted in the Dives, Magnet, (/amp Bird, and 
Tomboy mines. The quartz of the Silver Lake lodes frequently 
incloses chlorite, which gives it a green color, usually regarded as an 
indication of good ore. In some of the lodes the presence of minute 
included cryslals and grains of galena, sphalerite, tetrahedrite, argen- 
tite, various sulphobisnmthites, and oilier ore minerals results in a 
dark-clouded quartz in which the ore minerals are not recognizable 
with the naked eye. Such is the richest ore of the Ridgway mine 
(PL X, .4). Microscopic fluid inclusions are common, usually with 
gaseous bubbles. They arc frequent ly arranged along irregularly dis- 
posed curved surfaces in the quartz. 
In addition to quartz of the foregoing character, which has crystal- 
lized in open spaces, there occurs within and adjacent to many of the 
lodes, and especially in connection with the slocks of the Red Moun- 
tain district, a much more finely crystalline quartz, sometimes resem- 
bling a fine-grained quartzite, which has resulted from a partial or 
complete replacemenl of country rock by silica. As seen in thin sec- 
lion under the microscope, this quartz is associated with more or less 
sericite or kaolin, and sometimes alunite, in a eryptocrystalline 
mosaic. Such a mosaic often reveals Ihe outlines of the former crys- 
lals of feldspar, which have been metasomatically replaced, as more 
fully deseri bed on pages L14-131. 
As vein Idling, with of her gangue minerals and ore, quartz occurs 
in nearly all the productive Lodes of the quadrangle, but the relative 
amount of quartz and ore minerals varies widely between the highly 
siliceous gold ore of the Tomboy, showing to the eye insignificant 
mineralization, to the coarsely crystalline, heavy lead ore of the Royal 
Tiger and Iowa mines. In a few of the lodes occurring in rhyolite, 
vein quartz may be practically absent. It did not occur to any con- 
siderable extent with the ore stocks of the Red Mountain district, 
where the quartz is chiefly the result of metasomatic replacement of 
the country rock. 
Barite. — BaS0 4 . Orthorhombic. Massive, or in groups of diverg- 
ing tabular crystals. Cleaves perfectly in three directions. White. 
Transparent to opaque. Hardness, 3. Specific gravity, 4.5; whence 
common name "heavy spar." 
This is not nearly so important a gangue mineral in the Silverton 
quadrangle as quartz, but it occurs massive with the latter mineral 
in the veins in the Sultan Mountain monzonite mass, in the Royal 
Tiger, Melville, and probably other lodes in Silver Lake Basin, as a 
heavy vein in the Dives and Potomac claims, in the veins of Galena 
Mountain, where it has sometimes been replaced by pseudomorphous 
quartz, and in the Bonanza, Alaska, Tempest, Alabama, Old Lout, 
