Here's why:
* Calcite is a carbonate mineral. This means it contains the carbonate ion (CO3^2-).
* Hydrochloric acid (HCl) is an acid. Acids react with carbonates to produce carbon dioxide gas (CO2), water (H2O), and a salt.
* The reaction produces bubbles of CO2 gas. This is what causes the fizzing.
You can observe this reaction by dropping a piece of calcite (like a piece of limestone or marble) into a solution of hydrochloric acid. The fizzing and bubbling you see is the carbon dioxide being released.
