Acidic rock

Acidic rock is rock that is either siliceous, having a high content of silica (SiO₂), or rock with a low pH. The two definitions are not equivalent, e.g., in the case of basalt, which is never high in pH (basic), but is low in SiO₂. The term may be used in a third way, to refer to non-calcareous rocks, i.e., rocks testing negative for carbonate by not bubbling if a 10% solution of HCl is applied in a spot test.