andesitt

Andesitt is a volcanic rock term used in some languages to refer to andesite, an igneous rock of intermediate silica content. The name andesitt is commonly found in languages such as Norwegian and Swedish, where it designates the same rock type known elsewhere as andesite. The term derives from the Andes mountain range, where these rocks were first described and studied.

Mineralogy and texture characterise andesitt by a dominant plagioclase feldspar component, often calcium-rich to andesine, with lesser amounts of pyroxene or hornblende. Accessory minerals such as magnetite, ilmenite, and sometimes small amounts of biotite may occur; quartz is generally rare. Texturally, andesitt ranges from aphanitic to porphyritic, with small to moderately sized crystals that can form vesicular or dense rock depending on the eruption and cooling history. Its silica content typically falls in the mid-range for igneous rocks, around 57–63 percent SiO2.

Formation and occurrence: andesitt forms from magma of intermediate composition, commonly generated in subduction zone settings. It is a major constituent of volcanic arcs and continental margins, and is widespread in lands formed by subduction processes around the world. Classic examples include rocks associated with the Andean and Cascadian volcanic belts, among others.

Geological significance and uses: as an abundant volcanic rock, andesitt contributes to crustal diversity and is frequently exposed in volcanic domes and lava flows. It is commonly used as construction aggregate and, when fresh and dense, can be suitable for certain architectural or sculptural applications. In petrology, andesitt occupies an important position between basalt and rhyolite in the silica spectrum.