Trachyandesite

A cut block of trachyandesite lava from a volcano in Auvergne, France, used as building stone, forming part of the walls of Clermont-Ferrand Cathedral, France.

Trachyandesite is an extrusive igneous rock with a composition between trachyte and andesite. It has little or no free quartz, but is dominated by alkali feldspar and sodic plagioclase along with one or more of the following mafic minerals: amphibole, biotite or pyroxene. Small amounts of nepheline may be present and apatite is a common accessory mineral.

Trachyandesitic magma can produce explosive Plinian eruptions, such as happened at Tambora in 1815.

External links

• Photomicrograph of a thin section of trachyandesite from France, in crossed-polarised light

Volcanoes
Volcano types	Caldera Cinder cone Complex volcano Cryovolcano Fissure vent Lava cone Lava dome Maar Mud volcano Parasitic cone Pyroclastic cone Pyroclastic shield Rootless cone Shield volcano Somma volcano Stratovolcano Subglacial volcano Submarine volcano Supervolcano Volcanic cone Volcanic field (polygenetic · monogenetic)
Volcanic rocks	Volcanic rock Agglomerate Andesite Basalt Basaltic andesite Benmoreite Blairmorite Dacite Felsite Komatiite Latite Leucitite Nephelinite Obsidian Phonolite Phonotephrite Rhyodacite Rhyolite Tephriphonolite Trachyte Trachyandesite Trachybasalt Tuff
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