marble - large-grained gray marble - display specimen from the Lost Burro Formation
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This marble is a unit of the Devonian Lost Burro Formation. It is associated with cyclically bedded and vertically tilted limestone, field photos. It was quarried at the Valley Mine in Knight Canyon on the east slope of the Argus Range in the Panamint Valley, Inyo County, California, apparently along with dolomite for roofing or landscaping. The mine, operated by Metalline Industries of Grass Valley, California, has long been inactive. In the 1950s and '60s, gently-sloped ranch house roofs in Southern California were often covered with loose crushed white dolomite gravel.
Marble and dolomite can look similar. Marble is calcium carbonate, derived by metamorphism from limestone. When further metamorphism adds magnesium, the result is calcium-magnesium carbonate, dolomite.
In the field and in the lab these two metamorphic rocks can be identified by their differing reactions to dilute hydrochloric acid. Marble strongly effervesces. Dolomite effervesces weakly or not at all, and strongly only when powdered by a few taps of the geologist's hammer. The difference will be obvious to students in the lab.
It would be instructive to compare this marble with a large-crystal dolomite. It can also look, at first glance, like a granitic rock missing the dark minerals. The granitics will not effervesce and they are much harder.
The pencil is 5 1/2" long, for scale.
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