rhyoliittinen

Rhyoliittinen is the Finnish term for rhyolitic, an adjective used in geology to describe rhyolite-related magmas, rocks and volcanic products. Rhyolite is a felsic, silica-rich extrusive igneous rock. Its chemical composition typically contains 66–76% SiO2 and is enriched in alkali feldspar and quartz. The mineral assemblage commonly includes quartz and alkali feldspar (potassium feldspar), with plagioclase in lesser amounts; accessory minerals may include biotite, hornblende, zircon. Rhyolitic rocks are usually fine-grained (aphanitic) or porphyritic; in some cases they form glassy obsidian or vesicular pumice.

Rhyolitic magma forms at shallow crustal levels and is highly viscous, which favors explosive eruptions. Eruptions produce pyroclastic deposits such as rhyolitic tuff and ignimbrite, as well as lava domes built from rhyolite lava. The high viscosity also leads to crustal-tectonic processes leaving behind extensive rhyolitic lava flows in suitable settings.

Rhyolitic rocks occur in continental crust regions, particularly in volcanic arcs above subduction zones where crustal melting and differentiation generate felsic magmas. They are important for understanding crustal evolution, magma generation, and tectonic history. The term rhyoliittinen thus designates rocks, minerals or magmas with rhyolitic characteristics.