trachyandesite
Sign in to savethumb|upright=1.35|A cut block of trachyandesite lava from a volcano in Auvergne (region)|Auvergne, France, used as building stone, forming part of the walls of [[Clermont-Ferrand Cathedral, France]] thumb|upright=1.35|Trachyandesite is field S3 in the TAS diagram
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thumb|upright=1.35|A cut block of trachyandesite lava from a volcano in Auvergne (region)|Auvergne, France, used as building stone, forming part of the walls of [[Clermont-Ferrand Cathedral, France]] thumb|upright=1.35|Trachyandesite is field S3 in the TAS diagram
Trachyandesite is an extrusive igneous rock with a composition between trachyte and andesite. It has little or no free quartz, but is dominated by sodic plagioclase and alkali feldspar. It is formed from the cooling of lava enriched in alkali metals and with an intermediate content of silica.