MineralogyAn extrusive igneous rock composed mostly of alkali feldspar. It is usually light-colored and aphanitic (fine-grained), with minor amounts of mafic minerals, and is formed by the rapid cooling of lava enriched with silica and alkali metals.
It is the volcanic equivalent of syenite.
ContentPrimary: Alkali feldspar
Secondary:
Plagioclase, quartz, or feldspathoid.