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. [2]
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% Na2O > K2O + 2 for hawaiite. [3] [4] [5] The intrusive equivalent of trachybasalt is monzonite. [6]
Trachybasalt is not defined on the QAPF diagram, which classifies crystalline igneous rock by its relative content of feldspars and quartz. [3] [4] [5] However, the U.S. Geological Survey defines trachybasalt as a mafic volcanic rock (composed of over 35% mafic minerals) in which the quartz- feldspar- feldspathoid fraction of the rock is less than 20% quartz and less than 10% feldspathoid, and in which plagioclase is between 65% and 90% of the total feldspar content. [7]
Trachybasalt is common in continental volcanism and is also found on some ocean islands. [8] It is abundant at Mount Etna [9] and at Mount Taylor (New Mexico). [10] It has also been found on Gale crater on the planet Mars. [11]
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. [2]
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% Na2O > K2O + 2 for hawaiite. [3] [4] [5] The intrusive equivalent of trachybasalt is monzonite. [6]
Trachybasalt is not defined on the QAPF diagram, which classifies crystalline igneous rock by its relative content of feldspars and quartz. [3] [4] [5] However, the U.S. Geological Survey defines trachybasalt as a mafic volcanic rock (composed of over 35% mafic minerals) in which the quartz- feldspar- feldspathoid fraction of the rock is less than 20% quartz and less than 10% feldspathoid, and in which plagioclase is between 65% and 90% of the total feldspar content. [7]
Trachybasalt is common in continental volcanism and is also found on some ocean islands. [8] It is abundant at Mount Etna [9] and at Mount Taylor (New Mexico). [10] It has also been found on Gale crater on the planet Mars. [11]