rhyolitt

Rhyolitt, also known as rhyolite in English, is an extrusive felsic igneous rock with a high silica content and abundant alkali feldspar and quartz. It forms from the rapid cooling of high-silica magma at or near the Earth’s surface, producing a predominantly fine-grained, aphanitic texture, though some varieties are porphyritic with larger quartz or feldspar phenocrysts.

Rhyolitt is the volcanic equivalent of granite: both have similar chemical composition, but rhyolite crystallizes at the surface and thus has a much finer grain structure. The mineral assemblage typically includes quartz, alkali feldspar (such as orthoclase or sanidine), and plagioclase, with minor amounts of biotite or hornblende. SiO2 content is usually greater than 69 wt%.

Rhyolitt occurs in several forms, including lava flows, lava domes, and pyroclastic rocks such as rhyolitic tuffs and ignimbrites. In some cases, rhyolitic lava erupts and rapidly cools to form obsidian, a natural volcanic glass. The high viscosity and gas content of rhyolitic magma drive explosive eruptions and the production of pyroclastic deposits.

Geologically, rhyolitt is common in continental crust and is strongly associated with subduction-zone volcanic arcs. It is often linked to crustal melting and differentiation processes that generate silica-rich magmas.

Uses of rhyolitt are limited by its fragility and porosity, but it is sometimes quarried as a decorative or construction stone in suitable locations. Obsidian varieties have historical significance for tool-making due to their sharp edges when fractured.