What is Acid Test? An acid test is a controlled drop of dilute acid used to see if a mineral fizzes from a carbonate reaction. Calcite typically reacts readily, while dolomite may require a powdered spot to show a clear reaction. Collectors use an acid test to separate carbonates from similar-looking silicates and cements in the field. Test a tiny area and rinse afterward to prevent etching and residue.
For an Acid Test, start mild and step up only when needed because stronger acids can mark surfaces. If the reaction is weak, scratch and powder a pinpoint spot—fresh powder exposes more area and can reveal slow effervescence. Rinse and dry the sample after testing so your storage bags and labels don’t pick up acid residue. In your notes, record whether the fizz was immediate, slow, or only on powder because that distinction matters for identification.
Acid Test vs. bubbles from porous rock Trapped air can bubble when acid wets pores. Look for sustained fizz at the exact test spot.
Acid Test vs. carbonate dust contamination Carbonate dust on the surface can fizz. Scratch a clean spot and retest.
Acid Test vs. dolomite “no reaction” Dolomite may react weakly unless powdered. Note whether the test was on powder or a smooth face.
Acid Test vs. damaging a display face Acid can etch. Test an inconspicuous area or a small chip and rinse afterward.