trachybasalt

thumb|upright=1.35|Potassic trachybasalt from the July–August 2001 eruption of Mount Etna, Italy thumb|Satellite image of Bayuda volcanic field in Sudan where [[nepheline-rich trachybasalt lavas have been erupted during the Holocene epoch]] Trachybasalt is a volcanic rock with a composition between trachyte and basalt. It resembles basalt but has a high content of alkali metal oxides. Minerals in trachybasalt include alkali feldspar, calcic plagioclase, olivine, clinopyroxene and likely very small amounts of leucite or analcime.

==Description== thumb|TAS diagram 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.