Ans: The alkali mineral in rhyolite is sanidine, or less often orthoclase. It is scarcely anorthoclase. These feldspar minerals in rhyolite are present as phenocryst. The plagioclase is generally rich in sodium (oligoclase or andesine). The minerals such as cristobalite or tridymite are sometimes present along with the quartz. The accessory minerals found in the rhyolite are augite biotite, fayalite, and hornblende.