Potash feldspar/muscovite/quartz

The first minerals to crystallise, at highest temperatures and pressures, are poor in silicon (<50% Si02) and are rich in calcium, iron and magnesium and they form minerals, such as olivine and the pyroxenes, which make up the basic or mafic rocks. The acidic or silicic rocks are the last to form, are rich in silicon (>65% Si02) and are dominated by quartz, the potash feldspars and muscovite. 

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