Yes, geologists use acids to identify rocks, but not all the time. It's a specific test used for a particular type of rock.

Here's the breakdown:

* The Acid Test: Geologists use dilute hydrochloric acid (HCl) to test for the presence of calcium carbonate (CaCO3). This is the primary component of limestone and marble. When a drop of acid is placed on a rock containing calcium carbonate, it will fizz and bubble as carbon dioxide (CO2) gas is released.

* Why it works: The acid reacts with the calcium carbonate, breaking it down and releasing carbon dioxide. This fizzing reaction is a clear indicator that the rock contains calcium carbonate.

* Limitations: Not all rocks contain calcium carbonate. The acid test is not useful for identifying rocks like granite, basalt, or sandstone.

In summary: The acid test is a quick and easy way to determine if a rock contains calcium carbonate. It's a valuable tool for geologists, but it's only one test among many used for rock identification.