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Nepheline syenite is a holocrystalline plutonic rock that consists largely of nepheline and alkali feldspar. [1] The rocks are mostly pale colored, grey or pink, and in general appearance they are not unlike granites , but dark green varieties are also known.
Syenite from Corsica QAPF diagram that shows the quartz (Q), alkali feldspar (A), and plagioclase (P) composition of syenite Leucocratic variety of nepheline syenite from Sweden 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 ...
Phonolite is an uncommon shallow intrusive or extrusive rock, of intermediate chemical composition between felsic and mafic, with texture ranging from aphanitic (fine-grained) to porphyritic (mixed fine- and coarse-grained). Phonolite is a variation of the igneous rock trachyte that contains nepheline or leucite rather than quartz. [1]
For example, a syenite with significant nepheline present can be termed a nepheline-bearing syenite or nepheline syenite, with the term nepheline replaceable by any foid mineral. Such terminology is used in the Streckeisen ( QAPF ) classification of igneous rocks.
Nepheline, also called nephelite (from Ancient Greek νεφέλη (nephélē) 'cloud'), is a rock-forming mineral in the feldspathoid group – a silica-undersaturated aluminosilicate, Na 3 K Al 4 Si 4 O 16, that occurs in intrusive and volcanic rocks with low silica, and in their associated pegmatites.
Case hardening is a weathering phenomenon of rock surface induration.It is observed commonly in: felsic alkaline rocks, such as nepheline syenite, phonolite and trachyte; pyroclastic rocks, as pyroclastic flow deposit, fine air-fall deposits and vent-filling pyroclastic deposits; sedimentary rocks, as sandstone and mudstone.
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Litchfieldite (nepheline syenite gneiss) from Canaã Massif, Brazil. Litchfieldite is a rare igneous rock.It is a coarse-grained, foliated variety of nepheline syenite, [1] sometimes called nepheline syenite gneiss or gneissic nepeheline syenite. [2]