When dilute acid is dropped onto a mineral specimen and it effervesces (bubbles), which mineral is most likely present?

• A. Calcite (CaCO_3)
• B. Gypsum (CaSO_4 · 2H_2O)
• C. Halite (NaCl)
• D. Quartz (SiO_2)

Answer: (A)

Verified step by step guidance

1. Understand that effervescence (bubbling) when dilute acid is applied indicates a chemical reaction producing a gas, typically carbon dioxide (CO_2).
2. Recall that carbonates react with acids to produce CO_2 gas, water, and a dissolved salt. The general reaction is: \(\text{CaCO}_3 + 2\text{H}^+ \rightarrow \text{Ca}^{2+} + \text{CO}_2 + \text{H}_2\text{O}\).
3. Identify which mineral contains carbonate ions (CO_3^{2-}). Among the options, calcite (CaCO_3) contains carbonate ions and will react with acid to produce bubbles.
4. Recognize that gypsum (CaSO_4 \cdot 2\text{H}_2\text{O}), halite (NaCl), and quartz (SiO_2) do not contain carbonate ions and therefore do not effervesce with dilute acid.
5. Conclude that the mineral most likely present when effervescence occurs upon acid application is calcite (CaCO_3).