syenite
Sign in to savethumb|Syenite from Corsica thumb|upright=1.5|QAPF diagram that shows the [[quartz (Q), alkali feldspar (A), and plagioclase (P) composition of syenite]] thumb|Leucocratic variety of [[nepheline syenite from Sweden (särnaite)]] Syenite is a coarse-grained intrusive igneous rock with a general composition similar to that of granite, but deficient in quartz, which, if present at all, occurs in relatively small concentrations (< 5%). It is considered a granitoid. Some syenites contain larger proportions of mafic components and smaller amounts of felsic material than most granites; those are classe
Key facts
- Rock.name
- Syenite
- Rock.image
- Porphyritic syenite (Wausau Syenite Complex, Mesoproterozoic; Wausau, Wisconsin, USA) 2 - 52188157706.jpg
- Rock.type
- Igneous
- Rock.composition
- Plagioclase and K-Feldspars, depleted in quartz
- Rock.texture
- Phaneritic
- Rock.Equivalent
- Trachyte extrusively
- Rock.class
- Felsic
via Wikipedia infobox
Article
9 sectionsContents
- Composition
- Formation
- Partial melting
- Fractional crystallization
- Occurrence
- Etymology
- Episyenite
- See also
- References
thumb|Syenite from Corsica thumb|upright=1.5|QAPF diagram that shows the [[quartz (Q), alkali feldspar (A), and plagioclase (P) composition of syenite]] thumb|Leucocratic variety of [[nepheline syenite from Sweden (särnaite)]] Syenite is a coarse-grained intrusive igneous rock with a general composition similar to that of granite, but deficient in quartz, which, if present at all, occurs in relatively small concentrations (2) from which quartz has been severely depleted. This is often accompanied by strong enrichment in potassium and rare earth elements, leaving the altered rock a distinctive brick red color, or by albitization (enrichment in sodium), leaving the altered rock a conspicuous white color.
Episyenites are heterogenous in their properties, but all have experienced nearly complete disappearance of quartz at sub-solidus temperatures; that is, at temperatures below the melting point of the host rock. The formation of episyenites (episyenitization) typically takes place through leaching of quartz by mildly saline hydrothermal fluids, typically near a cooling intrusion. Because episyenitization usually takes place in granitoid rock and usually involves alkaline metasomatism (addition of alkali metal oxides to the rock) the result is a rock that has the mineral composition of an igneous syenite.