"Trachyte (TAS)"@en . "TRT"@en . "Trachyte (TAS)"@en . . . "stable"@en . . . . "Trachyte (TAS) - A type of trachytic-rock, classified using the total alkali silica (TAS) classification. The TAS classification may be used if the mineral mode of a normal fine-grained crystalline rock cannot be determined due either to the presence of glass or to the fine-grained nature of the rock. The definition of trachyte (TAS) is as shown in British Geological Survey Research Report RR/99/06, section 5.2 and figs. 17b, 20."@en . .