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Koch Shaft, Silver Mine District, Madison County, Missouri
Ex-Charley Cox Collection
Roughly 1.47 billion years ago the granites beneath what is now the St. Francois Mountains were finishing their long cool-down. The last fluids to leave that magma were the ones nothing else wanted — acidic, fluorine-rich, carrying tungsten and metals too oddly shaped to fit into ordinary feldspar. Those fluids pushed up into fractures and went to work on the granite around them, dissolving feldspar and replacing it with quartz and mica. The rock that came out the other side is greisen.
This piece is a vertical section straight through that alteration front, cut and polished on the face and cut flat on the base so it stands upright on a shelf without a stand.
In daylight the polished face is warm bronze and gold — dense micaceous flake catching light across the whole surface, shot through with dark metallic blebs and pockets, with a pale cream vein running the full height of the left edge. Under 365 nm longwave UV, that vein answers in bright blue-white: scheelite, calcium tungstate, the tungsten mineral that drew men into this hillside with picks and black powder. It reads as a clean, brilliant ribbon of light against a dead-black rock.
The mine: The Silver Mine district on the St. Francis River is unlike anything else in Missouri — argentiferous galena and tungsten mineralization hosted in Precambrian granite rather than the flat-lying carbonates of the lead belts. Workings go back to the 1870s under Knox and Einstein; by 1879 a stock company had built a dam across the river for water power, a furnace, dressing works, shaft houses, and put 200 to 300 men to work. The Koch Shaft is one of the district's smaller and far less-collected workings, now inside Mark Twain National Forest and closed with no plans to reopen. Specimens carrying a Koch Shaft label are considerably scarcer than Einstein, Apex, or Ozark material.
Provenance: Ex-Charley Cox Collection. Old Missouri material, out of the ground when these workings could still be walked.
Dimensions: 5.75" x 3.5" x 2" (146 x 89 x 51 mm)
Weight: 2 lbs 5.5 oz (1063 g)
Polished display face, cut base — stands on its own. Ships free, carefully dir="ltr" style="margin-top:0; margin-bottom:0;">KEYWORDS
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