The acid test: identifying carbonates safely in the field

A drop of dilute hydrochloric acid is the classic way to check whether something is a carbonate mineral like calcite. Calcite fizzes vigorously on contact, producing visible bubbles almost immediately. Dolomite is the classic look alike that often gets confused with calcite, it reacts much more slowly with dilute acid and sometimes only fizzes noticeably once the surface is scratched or powdered first. Plain white vinegar is much weaker than lab grade hydrochloric acid but can still show a slow reaction on powdered calcite if you do not want to keep stronger acid around. A few real safety points matter here, always wear eye protection, work in a ventilated area, use the smallest amount of acid that will show a reaction (a single drop on an inconspicuous spot), and never test a polished or display quality specimen this way since acid will etch the surface permanently. Rinse and neutralize any test area afterward and dispose of used acid properly rather than down a drain.