What is the dominant factor that determines the crystal size in igneous rocks? Compare granit to rhyoliticour explanation. The Role of Silica Content in Determining Crystal Size in Igneous Rocks

The Role of Silica Content in Determining Crystal Size in Igneous Rocks

The crystal size of igneous rocks is largely determined by the silica content of the magma. Silica, or silicon dioxide (SiO2), is the most abundant mineral in the Earth’s crust and is the major component of magma. The more silica that is present in the magma, the higher the viscosity of the magma and the slower the rate of cooling. As a result, the magma has more time to form large crystals. Granite is an igneous rock that is composed of between 10-60% silica, while rhyolite is composed of between 60-70% silica (Friedrich, 2017; Allaby, 2018). As such, rhyolite typically has larger crystals than granite due to its higher silica content and a slower rate of cooling. In addition to the silica content, the rate of cooling also plays an important role in determining the crystal size of igneous rocks. If the magma cools quickly, the crystals have less time to form and will be much smaller. This is often the case with basalt, an igneous rock composed of 45-54%. Cont…