name the processes and explain how sandstone changes into quartz
by definition, granite has to be at least 20% quartz, and if it's more than 60% they call it something else. It has anywhere from 20% to 60% quartz.
By definition, granite is an igneous rock with at least 20% quartz by volume. Granite differs from granodiorite in that at least 35% of the total feldspar in granite is alkali feldspar (orthoclase or microcline) as opposed to plagioclase; it is the alkali feldspar that gives many granites a distinctive pink colour. Generally, granites are composed of more alkali feldspar than plagioclase, but this isn't always the case - there is potential of much variation - some white granites may have more plagioclase than orthoclase though pink granites are rich in orthoclase. A typical quartz / alkali feldpar (othoclase / microcline) / plagioclase percentages would be 35% / 35% / 15%. The remaining 15% would be made up by mica accessory minerals.
