Syenogranite is a fine to coarse grained intrusive

igneous Igneous rock ( ), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial ...

rock of the same general composition as

granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...

. They are characteristically

felsic In geology, felsic is a grammatical modifier, modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz.Marshak, Stephen, 2009, ''Essentials of Geology,'' W. W. Norton & Company, 3rd ed. It is contrasted ...

. The

feldspar Feldspar ( ; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagiocl ...

component of syenogranite is predominantly

alkaline In chemistry, an alkali (; from the Arabic word , ) is a basic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The ...

in character (usually

orthoclase Orthoclase, or orthoclase feldspar ( endmember formula K Al Si3 O8), is an important tectosilicate mineral which forms igneous rock. The name is from the Ancient Greek for "straight fracture", because its two cleavage planes are at right angles ...

). For example, the syenogranite in the Salmon Mountains in Idaho is pink to tan and composed of 45–55% alkali feldspar, 15–20%

plagioclase Plagioclase ( ) is a series of Silicate minerals#Tectosilicates, tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continu ...

, 15–20%

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

, 5–8%

biotite Biotite is a common group of phyllosilicate minerals within the mica group, with the approximate chemical formula . It is primarily a solid-solution series between the iron- endmember annite, and the magnesium-endmember phlogopite; more al ...

, 3–5%

hornblende Hornblende is a complex silicate minerals#Inosilicates, inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common ...

, and accessory

magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula . It is one of the iron oxide, oxides of iron, and is ferrimagnetism, ferrimagnetic; it is attracted to a magnet and can be magnetization, magnetized to become a ...

(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 Muscovite (also known as common mica, isinglass, or potash mica) is a hydrated phyllosilicate mineral of aluminium and potassium with formula KAl2(Al Si3 O10)( F,O H)2, or ( KF)2( Al2O3)3( SiO2)6( H2O). It has a highly perfect basal cleavage y ...

and

rutile Rutile is an oxide mineral composed of titanium dioxide (TiO2), the most common natural form of TiO2. Rarer polymorphs of TiO2 are known, including anatase, akaogiite, and brookite. Rutile has one of the highest refractive indices at vis ...

as additional accessories in the syenogranite. Some syenogranite contain rare idiomorphic

amphibole Amphibole ( ) is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is ...

(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 A massif () is a principal mountain mass, such as a compact portion of a mountain range, containing one or more summits (e.g. France's Massif Central). In mountaineering literature, ''massif'' is frequently used to denote the main mass of an ...

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

, the syenogranite is a coarse-grained rock composed of

microcline Microcline (KAlSi3O8) is an important igneous rock-forming tectosilicate mineral. It is a potassium-rich alkali feldspar. Microcline typically contains minor amounts of sodium. It is common in granite and pegmatites. Microcline forms during s ...

, quartz, hornblende, and rare clinopyroxene, together with allanite, as essential minerals (Benjamin et al., 1998).

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. 2

* 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 Surve

* 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. 5–2

Plutonic rocks {{petrology-stub

See also

References