magnesite with biotite flakes - teaching hand specimen
Magnesite, magnesium carbonate, MgCO3, can be earthy or crystalline. This earthy magnesite was formed through hydrothermal alteration of Miocene (?) lake beds, though it can also form in irregular veins and masses through the alteration of serpentine by water containing carbonic acid. Biotite in the lake bed sediments was not altered and shows up as black flakes in these specimens.
The Kramer Hills magnesite deposit was explored in the 1930s by the Ball (Red Seal) Chemical Company. A number of prospects have been opened since then, but it appears that commercial production was small. It has a commercial application in the manufacture of brick and furnace linings. The magnesite occurs in association with a tan chert that we often have in stock.
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