Passing the Acid Test

Dilute hydrochloric acid is recommended for the acid test. In the field, a drop of acid from a shatterproof bottle is a quick way to distinguish limestone from other rocks and calcite from other minerals. The bubbles are carbon dioxide gas. Vinegar (acetic acid), a weaker acid, also can be used to tell calcite. But a major question in the field is distinguishing calcite (CaCO₃) from the mineral dolomite (CaMg(CO₃)₂) and limestone from dolomite rock. These look nearly identical, and vinegar is not very good for that acid test.