Rhyolite

**Petrology:** This acidic volcanic rock contains abundant phenocrysts of quartz, pink potassic feldspar and white acid plagioclase associated with mafic minerals (biotite and amphibole). Light-coloured fragments of volcanic glass are scattered in the rock.

**Genesis:** Rhyolite can be considered as the extrusive equivalent to the plutonic granite rock. Due to their high content of silica and low iron and magnesium contents, rhyolites are created from highly viscous lavas. They also occur as breccias or in volcanic plugs and dikes. Rhyolites that cool too quickly to grow crystals form a natural glass (obsidian). Many eruptions of rhyolite are highly explosive and the deposits may consist of fallout tuff or of ignimbrites.

## Keywords
stone