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The Acid Test


Every serious field geologist carries a small bottle of 10 percent hydrochloric acid to perform this quick field test, used to distinguish the most common carbonate rocks, dolomite and limestone (or marble, which may be composed of either mineral). A few drops of the acid are put on the rock, and limestone responds by fizzing vigorously. Dolomite fizzes only very slowly. Here are some pictures made in a more controlled setting.

Hydrochloric acid (HCl) is available in hardware stores as muriatic acid, for use in cleaning stains from concrete. For geological field use, the acid is diluted to 10 percent strength and kept in a small strong bottle with an eyedropper. This gallery also shows the use of household vinegar, which is slower but suitable for occasional or amateur users.

Images 1-7 of 7
The classic acid testCalcite in Hydrochloric AcidThe classic dolomite reactionDolomite in Hydrochloric AcidThe real thingCalcite in Acetic AcidCould be eitherMystery Carbonate
Not calciteCalcite Test FailsDefinitely a carbonateCrushed Carbonate MineralA slow burnDolomite in Acetic Acid
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