Most of the rocks of the Earth 's crust have quartz ( crystalline SiO2 ) , feldspar , mica , chlorite , kaolin , calcite , epidote , olivine , augite , hornblende , magnetite , hematite , limonite and a few other minerals . The vast majority of the rocks of the Earth 's crust consist of quartz ( crystalline SiO2 ) , feldspar , mica , chlorite , kaolin , calcite , epidote , olivine , augite , hornblende , magnetite , hematite , limonite and a few other minerals .