Extrusive Igneous Rock - Rhyolite
By Alec Augustine
It is usually pink or gray in color with grains so small that they are difficult to observe without a hand lens.
Contains gems such as the Fire opal, and other stuff such as crystals and glassy material.
Uses and How and Where it is Formed
Can be used as aggregate, fill, etc. in the construction and roading industries.
Many rhyolites form from granitic magma that has partially cooled in the subsurface.
Rhyolite is rarely produced at oceanic eruptions.
The large crystals that formed beneath the surface are called phenocrysts and the small crystals formed at the surface are called groundmass.