acid rock Igneous rock containing more than about 60% Silica (SiO₂) by weight, most of the silica being in the form of silicate minerals, but with the excess of about 10% as free quartz. Typical acid rocks are granites, granodiorites, and rhyolites. Compare BASIC ROCK; and INTERMEDIATE ROCK. See also ALKALINE ROCK.

acid rock Igneous rock that contains more than about 60 per cent silica (SiO₂) by weight, most of the silica being in the form of silicate minerals, but with the excess of about 10 per cent as free quartz. Typical acid rocks are granites, granodiorites, and rhyolites. See also alkaline rock; compare basic rock and intermediate rock.