Obsidian, which is rhyolitic volcanic glass, has been used for tools from prehistoric times to the present day because it can be shaped to an extremely sharp edge.

Rhyolite is an extrusive igneous rock, formed from magma rich in silica that is extruded from a volcanic vent to cool quickly on the surface rather than slowly in the subsurface.

It is generally light in color due to its low content of mafic minerals, and it is typically very fine-grained (aphanitic) or glassy.

Rhyolite is high in silica and total alkali metal oxides, placing it in the R field of the TAS diagram.

[10]: 22  Rhyolitic ash flow tuffs are the only volcanic product with volumes rivaling those of flood basalts.

[9]: 20 Rhyolites that cool too quickly to grow crystals form a natural glass or vitrophyre, also called obsidian.

[13] Slower cooling forms microscopic crystals in the lava and results in textures such as flow foliations, spherulitic, nodular, and lithophysal structures.

As a result of their increased fluidity, they are able to form small-scale flow folds, lava tubes and thin dikes.

HSRs are the most evolved of all igneous rocks, with a composition very close to the water-saturated granite eutectic and with extreme enrichment in most incompatible elements.

The thicker continental crust gives the rising magma more opportunity to differentiate and assimilate crustal rock.

[25] Small volumes of rhyolite are sometimes erupted in association with flood basalts, late in their history and where central volcanic complexes develop.

[26] The name rhyolite was introduced into geology in 1860 by the German traveler and geologist Ferdinand von Richthofen[27][28][29] from the Greek word rhýax ("a stream of lava")[30] and the rock name suffix "-lite".

[35] Pumice, also typically of rhyolitic composition, finds important uses as an abrasive, in concrete,[36] and as a soil amendment.