Article
Article
Syenite
Article By:
Chapman, Carleton A. Department of Geology, University of Illinois, Urbana, Illinois.
Last reviewed:December 2019
DOI:https://doi.org/10.1036/1097-8542.673300
A phaneritic (visibly crystalline) plutonic rock with granular texture composed largely of alkali feldspar (orthoclase, microcline, usually perthitic) with subordinate plagioclase (oligoclase) and dark-colored (mafic) minerals (biotite, amphibole and pyroxene). If sodic plagioclase (oligoclase or andesine) exceeds the quantity of alkali feldspar, the rock is called monzonite. Monzonites are generally light to medium gray, but syenites are found in a wide variety of colors (gray, green, pink, red), some of which make the material ideal for use as ornamental stone.
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