Mineral Class: Felsic
Crystal System: Trigonal
Hardness: 6
Luster: Earthy
Diaphaneity: Opaque
Colors: Gray, Pink, Red, Black
Symbolizes: Strength
Source: Australia, Mexico, USA

Rhyolite, an extrusive igneous rock,formed from magma rich in silica,is the mostsilica-rich of all volcanic rocks. It is generally glassy or fine-grained in texture, but may be porphyritic, containing larger mineral crystals in an otherwise fine-grained rock. The mineral assemblage is predominantly Quartz, Sanidine and Plagioclase. It is the extrusive equivalent to granite. Rhyolitic tuff has been extensively used for construction. Obsidian, a form of rhyolitic volcanic glass that cooled too quickly, has been used for tools from prehistoric times to the present day because it can be shaped to an extremely sharp edge. Rhyolitic pumice finds use as an abrasive, in concrete, and as a soil amendment.