By Andrew Alden, About.com Guide

Generally the carbonate minerals
are found at or near the surface. They represent the Earth's largest
storehouse of carbon. They all are on the soft side, from hardness 3 to 4
on the Mohs hardness scale. Every
serious rockhound and geologist takes a little vial of hydrochloric
acid into the field, just to deal with the carbonates. The carbonate
minerals shown here react differently to hydrochloric acid, as follows:
Aragonite bubbles strongly in cold acid
Calcite bubbles strongly in cold acid
Cerussite does not react (it bubbles in nitric acid)
Dolomite bubbles weakly in cold acid, strongly in hot acid
Magnesite bubbles only in hot acid
Malachite bubbles strongly in cold acid
Rhodochrosite bubbles weakly in cold acid, strongly in hot acid
Siderite bubbles only in hot acid
Smithsonite bubbles only in hot acid
Witherite bubbles strongly in cold acid

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