marble - teaching hand specimen of large-grained white marble
This marble is pure white with very large crystals. It is a unit of the Late Proterozoic Johnnie Formation and is being mined for cement-making. These specimens were collected at the Piercy Quarry near Victorville, San Bernardino County, California.
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.
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