TAS classification

The TAS diagram ( TAS = total alkali vs. Silica) by Mike le Bas is used for the classification of igneous rocks ( volcanic effusions ) based on the chemical composition of the whole rock. There are the contents plotted in weight percent Na2O K2O in the Y-direction against SiO2 in the X direction.

This diagram is used when a determination of the modal mineral inventory of the rock, as required for classification in the Streckeisen diagram is not possible. This is common in fine-grained or glassy volcanic rocks of the case.

TAS diagram

The TAS diagram is divided into 15 fields. The titles of the fields, that is, the names of the rocks, predominantly have an equivalent in the Streckeisen diagram. Specifically, these are:

Sodium kingdom here means Na2O > K2O, potassium- rich K2O > Na2O