Now, when I finally found the Colorado Springs group I had forgotten my camera. So, I have substituted some beautiful Mexican Gold Poppies blooming in the desert. They are a spring delight.
Serpierite is another one of those nice blue copper minerals ranging from a light to a dark sky blue with some almost a blue-green turquoise color. It occurs in fluffy tufts, crusts, or aggregates of very tiny, lath-like vitreous crystals. These small crystals are transparent and some almost lack color. They are somewhat confusing, at least to a soft rocker like me, in that the crystals are elongated along axis a and not the “usual” c axis. In fact, they are flattened along the c axis to produce the lath-like shape. Serpierite fractures easily into splinters and seems quite soft (~2 Mohs). I tried an unglazed porcelain plate and the mineral essentially leaves a white streak.
Serpierite is a member of the small Devilline Group. I have a small specimen of devilline [CaCu4(SO4)(OH)6-3H2O] where the small tuft of platy crystals are essentially impossible for me to distinguish from serpierite. As one can observe devilline is missing the zinc of serpierite. Add some cadmium in place of some of the calcium in serpierite and the mineral becomes aldridgeite (structure the same: isostructural).
Serpierite is a secondary mineral and found in the hydrothermal zone associated with copper and zinc deposits. For example, at the type locality of serpierite in the Lavrion District of Greece, there are numerous primary copper minerals and primary zinc minerals such as sphalerite.
I have three specimens of serpierite from different localities and all are somewhat different: Lavrion District, Greece; Creole Mine, Beaver County, Utah; Bay Horse District, Challis, Custer County, Idaho.
Photomicrograph of serpierite collected from its type locality at the Serpieri Mine, Lavrion District, Greece. Width FOV ~3 mm.
Photomicrograph of rosettes of lath-like crystals of serpierite collected from the Creole Mine, Beaver County, Utah. Width FOV ~1 cm.
Photomicrograph of numerous platy lathes of serpierite? Collected from the Bay Horse Mine, Challis, Custer County, Idaho. Width FOV ~7 mm.
The rocks examined at the proposed mine were part of a thick section of something like 35,000 feet of Paleozoic marine rocks that have an extremely complex stratigraphic and structural history (Hobbs and others, 1991). About the only fossils I remember finding (but again my memory sometimes fades) were numerous graptolites in the black shales. It was sort of eerie driving through a deserted “ghost town” in remarkably good shape. The area was privately owned and we did not stop to explore.
Part of the Bay Horse Mining District now incorporated into the Land of Yankee Fork State Park. Photo courtesy of www.deq.idaho.gov.
Since I visited the area the State of Idaho made a great decision and purchased the Bay Horse area and renamed it the Land of Yankee Fork State Park. I look forward to returning. And, I never paid much attention to note if the fluorspar mine was ever completed.
My third specimen of serpierite has an older looking label stating it was collected in the Bay Horse area at Challis, Idaho. However, the descriptions of serpierite at www.mindat.org do not recognize the mineral at Bay Horse. But I did find a reference in the Handbook of Mineralogy, www.handbookofmineralogy.com noting the occurrence of serpierite from the Bay Horse Mine at Challis. Maybe? Maybe not?
Hobbs, S.W., W.H. Hays, and D.H. Mcintyre, 1991, Geologic map of the Bayhorse Area, Central Custer County, Idaho: USGS Miscellaneous Investigations Series Map I-1882 pamphlet.
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