Trachyandesite

It is formed from the cooling of lava enriched in alkali metals and with an intermediate content of silica.

[4] The Eyjafjallajökull 2010 eruption (VEI-4[5]), which disrupted European and transatlantic air travel from 15-20 April 2010,[6] for some time was dominated by trachyandesite.

[8][3] When it is possible to identify the minerals present, trachyandesite is characterized by a high content of sodic plagioclase, typically andesine, and contains at least 10% alkali feldspar.

[2] Trachyandesite is not a recognized rock type in the QAPF classification, which is based on the actual mineral content.

[10] The 1982 El Chichón eruption produced trachyandesite pumice rich in anhydrite, and released 2.2 × 107 metric tons of sulfur.

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 field S3 in the TAS diagram