Occurrence of quartz in high amounts makes a rock

The occurrence of quartz in high amounts makes a rock acidic. Rocks like granite, microgranite, and rhyolite rich in silica are acidic rocks and contain the minerals quartz and feldspar.
Acidic rocks refer to the chemical composition of igneous rocks that has 63% weight % SiO₂ content. It usually contains more than 20% of free quartz.