The Painted Rock Mountains lay southwest of Phoenix,
Arizona, approximately 75 miles west of Casa Grande, Arizona,
along I-8 and near Gila Bend. It is a
small range, as mountains go, perhaps 12 miles long and up to 4 miles
wide. It is one of those typical Arizona
Basin and Range chains with high hills containing both intrusive and extrusive
igneous rocks, including basalt flows and thick pyroclastic beds, surrounded by
fans of eroded alluvium. There appears
to be numerous small faults but perhaps not the large bounding normal faults
that I am familiar with in the Utah ranges.
The name comes from numerous petroglyph sites created by members of the
Hohokam Culture (mostly). The Hohokam evidently
lived along the Gila River (~0-1450 AD), now usually dry or intermittent, but at
one time a nice stream. The Gila heads in the mountains of western New Mexico
and flows west toward Gila Bend finally emptying into the Colorado River at
Yuma. Rumor has it that at one time fairly large boats could navigate all the
way from the mouth to Phoenix!
The mountains contain one of the best known specimen
mines in Arizona—the Rowley Mine. Now
inactive for mining (last produced in 1943) the Rowley produced copper
(covellite, malachite, chalcocite), lead (anglesite, galena), iron (hematite)
and minor amounts of gold, silver, molybdenum, vanadium, and fluorite, and even
smaller amounts of barium and vanadinite.
However, what the Rowley really produces, or did produce, are wulfenite
crystals and “balls” of red to orange to yellow mimitite. Jones (2011) reported that the crystals of
both mimitite and wulfenite are found in the cracks and crevices of shattered barite
veins. MinDat lists 47 valid minerals
from the Rowley including caledonite (lead and copper sulfate-carbonate).
Photomicrographs of tiny caledonite crystals collected Rowley Mine, Arizona. Width FOV ~3 mm.
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Caledonite [Cu2Pb5(OH)6CO3(SO4)3]
is another one of those brightly colored (blue to green) minerals that is found
in the secondary oxidized zone of lead-copper deposits. The crystals are usually quite small, often
striated prismatic, but sometimes aggregates or tabs. It is rather soft at 2.5-3.0 (Mohs),
translucent, a vitreous luster and has a green-white to blue-green streak. Caledonite is a rare mineral; its classic
locality in Arizona is the Mammoth-St. Anthony (Tiger) Mine near the north end
of the Santa Catalina Mountains.
REFERENCES CITED
Jones, B, 2011, The Frugal Collector, Volume 1: Miller Magazines, Ventura, CA.
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