aragonite - "cave calcite" - El Potosi Mine, Santa Eulalia Mining District, Chihuahua - hand/display specimen
Aragonite is a pseudomorph of calcite, with the same chemical formula, calcium carbonate, but a different crystal structure. When carbonated groundwater contains calcium, it most commonly precipitates calcite when cold and aragonite, when hot.
Sometimes called "cave calcite," this aragonite comes from the Potosi Mine in the Santa Eulalia Mining District, Chihuahua, Mexico. The silver, lead, zinc and copper ores in this mine are associated with thick-bedded limestones overlain by a series of rhyolite flows and tuffs. In 1912, miners broke into a cavern lined with cave calcite forms similar to these specimens. In subsequent years, numerous cavities have been discovered, with at least some specimens extracted before the cavern was destroyed by mining.
As described in 1925 by mining engineer Carl Millikan, "one cave, the 'Gypsum' cave, when opened, presented a fairyland-like scene. Pure dazzling white, filled with crystals of all shapes and sizes, it was a bonanza for specimens of everything - but ore."
One specimen is shown twice. Tips of this specimen, shown front and back, (black pencil and three coins) fluoresce bright green under shortwave ultraviolet.
The pencil is 5.5" long, for scale.
Select a specimen: When more than one specimen is shown, you can select a particular specimen by telling us what is in the photo with it, a black mechanical pencil, or pencil plus some number of coins, or you can let us make the selection.
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