Trachyandesite is an effusive igneous rock intermediate in composition between trachyte and andesite, composed of plagioclase (andesine-oligoclase), K-feldspar, and one or more mafic minerals (biotite, amphibole, pyroxene). Trachybasalt is an effusive igneous rock intermediate in composition between trachyte and basalt, composed of calcic plagioclase, K-feldspar (commonly sanidine) with augite, olivine, and possibly minor analcime or leucite. Both rock types have been variously equated with one another and with latite; also, trachyandesites have been equated to latites plus latite-andesites and trachybasalt to latite and latite-basalt. Trachydolerite , an alkali basalt with orthoclase or anorthoclase, labradorite, and a small proportion of field-spathoids, and a chemical composition intermediate between trachyte and basalt, has also been used as a synonym of trachybasalt.
Rocks on a direct compositional line from (alkalic) basalt to (sodic) trachyte are hawaiite, mugearite, and...
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Bibliography
Hall, A., 1987, Igneous Petrology. Harlow, U.K.: Longman.
Middlemost, E. A. K., 1985, Magmas and Magmatic Rocks. Harlows, U.K.: Longman.
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© 1989 Van Nostrand Reinhold
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Bowes, D.R. (1989). Trachyandesite, trachybasalt . In: Petrology. Encyclopedia of Earth Science. Springer, Boston, MA. https://doi.org/10.1007/0-387-30845-8_243
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DOI: https://doi.org/10.1007/0-387-30845-8_243
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