Syenogranite

Syenogranite is a fine to coarse grained intrusive igneous rock of the same general composition as granite. They are characteristically felsic.

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The feldspar component of syenogranite is predominantly alkaline in character (usually orthoclase). For example, the syenogranite in the Salmon Mountains in Idaho is pink to tan and composed of 45–55% alkali feldspar, 15–20% plagioclase, 15–20% quartz, 5–8% biotite, 3–5% hornblende, and accessory magnetite (Evans and Green, 2003).

Syenogranite is similar to syenite, however the major difference is its higher content of quartz (15-25%) usually at the expense of some alkali feldspar (45-50%), the domination of biotite over hornblende and the presence of muscovite and rutile as additional accessories in the syenogranite. Some syenogranite contain rare idiomorphic amphibole (Fe-hornblende and Fe-edenite), biotite (annite 25%-35%), plagioclase (An₃), along with K-feldspar and quartz. (Mafti, 2001).

In the Sao Jose do Campestre Massif in Brazil, the syenogranite is a coarse-grained rock composed of microcline, quartz, hornblende, and rare clinopyroxene, together with allanite, as essential minerals (Benjamin et al., 1998).

See also

• syenite
• monzogranite
• granite

References

• Bley, Benjamin, Peter Christian Hackspacher, Elton Luizdantas, and William Randall Van Schmus. (1998) "Archean Accretion in the Sao Jose do Campestre Massif, Borborema Province, Northeast Brazil." Revista Brasileirade Geociencias, Vol. 28[1]
• Karl V. Evans and Gregory N. Green (2003) “Geological Map of the Salmon National Forest and Vicinity, East-Central Idaho.” U.S. Department of the Interior, U. S. Geological Survey.[2]
• Mafti, Mohammed Rashad H. (2001) "Age, Geochemistry and Origin of the Peraluminous A-Type Granitoids of the Ablah-Shuwas Pluton, Ablah Graben Arabian Shield." Faculty of Earth Sciences, King Abdulaziz University, Acta Mineralogica-Petrographica, Vol. 42, pp. 5-20.[3]