highlighting the trachybasalt field An
aphanitic (fine-grained) igneous rock is classified as trachybasalt when it has a silica content of about 49% and a total alkali metal oxide content of about 6%. This places trachybasalt in the S1 field of the
TAS diagram. Trachybasalt is further divided into sodium-rich
hawaiite and potassium-rich
potassic trachybasalt, with
wt% > + 2 for hawaiite. The intrusive equivalent of trachybasalt is monzonite. Trachybasalt is not defined on the
QAPF diagram, which classifies crystalline igneous rock by its relative content of
feldspars and
quartz. ==Occurrence==