Rhyolite is an extrusive igneous rock that forms when lava rich in silica cools quickly on the surface of the Earth. It has a fine-grained texture, meaning that its crystals are not visible to the naked eye. This distinguishes it from granite, which is a similar rock formed by slow-cooling magma (molten rock that is still below the surface) deep within the Earth.

The main components of rhyolite are silicon dioxide (SiO2), aluminium oxide (Al2O3), and trace amounts of other elements such as potassium, sodium, calcium, iron, and magnesium. When the lava rises towards the surface, these molten elements cool rapidly into a mineral composition resembling feldspar and granite.