A coarse-grained plutonic rock generally devoid of quartz (up to 10 percent quartz in quartz syenites), syenite is a light-colored rock often confused with granite. This intermediate rock, with total silica between 55 and 65 percent, is principally formed of alkali feldspar and/or sodic plagioclase and is usually associated with biotite, amphibole, or pyroxene.

TEXTURE A coarse-grained rock with all minerals visible to the naked eye and with grains generally the same size. It is sometimes porphyritic—where larger crystals are enclosed by a finer-grained matrix. Crystals are mainly anhedral to euhedral.

ORIGIN Usually forms in minor intrusions, dykes, and sills, often associated with granites.

Group: IGNEOUS

Origin: Intrusive

Grain size: Coarse

Crystal shape: Anhedral, Euhedral

Classification: Intermediate

Occurrence: Pluton, Dyke, Sill

Color: Light, Dark