Carbonate minerals such as calcite and dolomite can be positively identified by?

• A. An acid test
• B. A hardness test
• C. A magnetism test
• D. A streak test

Answer: (A)

The key idea is that carbonate minerals react with acids to produce carbon dioxide gas. When a drop of dilute hydrochloric acid is placed on calcite or dolomite, bubbles of CO2 form as the mineral dissolves in the acid, a reaction written roughly as CaCO3 + 2HCl → CaCl2 + CO2 + H2O (and a similar reaction for dolomite, CaMg(CO3)2). This fizzing, or effervescence, is a distinctive, quick indicator of carbonates and is routinely used to identify minerals like calcite and dolomite in the field or lab. Dolomite can fizz more slowly or require powdered material or slightly warmer acid to see fizz, but the reaction still occurs, reinforcing its diagnostic value. Other tests like hardness, magnetism, or streak aren’t as definitive for carbonates: hardness values can overlap with many minerals, magnetism is rare in carbonates, and a white streak is common to numerous minerals, so they don’t reliably signal carbonate minerals.