2012-7-25 · limestone . and. marble. Very important for CCS! Calcite (CaCO 3) CaCO 3 + 2H+ = Ca2+ + CO 2 + H 2. O. Smithsonite (ZnCO 3) Oxides. Compounds of metallic cations and oxygen. Important for many metal . ores. needed to make things (e.g., iron, chromium, titanium) Ores are economically useful (i.e., possible to mine) mineral deposits.