A proposal by the IUGS Subcommission on the Systematics of Igneous Rocks for a chemical classification of volcanic rocks based on the total alkali silica (TAS) diagram

Abstract The IUGS Subcommission on the Systematics of Igneous Rocks recommends that volcanic rocks should be classified on a non‐genetic basis using the total alkali silica (TAS) diagram. This is divided into 14 fields, three of which contain two root names which are separated according to other chemical criteria, giving the following 17 root names: basalt, basaltic andesite, andesite, dacite, rhyolite, alkali rhyolite, trachybasalt, trachyandesite, trachyte, alkali trachyte, picrobasalt, basanite, tephrite, phonotephrite, tephriphonolite, phonolite and foidite. Using other simple parameters, trachybasalt may be further divided into the sub‐root names of hawaiite and potassic trachybasalt, and trachyandesite may be further divided into the sub‐root names of mugearite, shoshonite, benmoreite and latite. Key words: chemical classificationvolcanic rock classificationTAS classificationIUGS Subcommissiontotal alkali silica diagram