Silica content
Silica is found in most of Earth's minerals. Silica is formed when oxygen and silicon interact. Silica is in magma and lava. Since silica is in magma and lava this effects the type of rock that is made. Lava that has a LOW silica content usually creates dark-colored rocks. Magma with a HIGH silica content usually creates light colored rocks. Granite is a good example of a rock with high silica. Granite has high silica but this rocks color is determined by its mineral composition.