Granitoid

Granite rock hand-sized sample

A granitoid is a generic term for a diverse category of coarse-grained igneous rocks that consist predominantly of quartz, plagioclase, and alkali feldspar.[1] Granitoids range from plagioclase-rich tonalites to alkali-rich syenites and from quartz-poor monzonites to quartz-rich quartzolites.[2] As only two of the three defining mineral groups (quartz, plagioclase, and alkali feldspar) need to be present for the rock to be called a granitoid, foid-bearing rocks, which predominantly contain feldspars but no quartz, are also granitoids.[2] The terms granite and granitic rock are often used interchangeably for granitoids; however, granite is just one particular type of granitoid.

Granitoids are diverse; no classification system for granitoids can give a complete and unique characterization of the origin, compositional evolution, and geodynamic environment for the genesis of a granitoid. Accordingly, multiple granitoid classification systems have been developed such as those based on: geochemistry, modal content,[jargon] emplacement depth, and tectonic regime.

  1. ^ "USGS: Mineral Resources On-Line Spatial Data: Granitoid".
  2. ^ a b Streckeisen, A. (1974). "Classification and Nomenclature of Plutonic Rocks: Recommendations of the IUGS Subcommission on the Systematics of Igneous Rocks". Geologische Rundschau (in German). 63 (2): 773–86. Bibcode:1974GeoRu..63..773S. doi:10.1007/BF01820841. S2CID 130569261.