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Nepheline syenite is a holocrystalline plutonic rock that consists largely of nepheline ... Thin section image of the nepheline syenite of the Intrusive Complex of ...
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.
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 classification of igneous rocks. [2]
The composition of the Nepheline-Sodalite Syenite ranges from >5% mafic minerals and 20% feldspathoids (nepheline and sodalite), to 20% mafic minerals and >5% feldspathoids. The remainder of the composition is perthitic feldspar. [1] [2] Thin section microphotographs of the Nepheline-Sodalite Syenite in both PPL and XPL are shown.
Crossed polarized light image of melilite in Moiliili lava flow, Moiliili Quarry, Honolulu, O‘ahu, Hawai‘i surrounded by matrix of granular nepheline and volcanic glass. This rock (nepheline-melilite basalt) was erupted during rejuvenated volcanism on O‘ahu. Melilite refers to a mineral of the melilite group.
Phonolite is a variation of the igneous rock trachyte that contains nepheline or leucite rather than quartz. [1] It has an unusually high (12% or more) Na 2 O + K 2 O content, defining its position in the TAS classification of igneous rocks. Its coarse grained (phaneritic) intrusive equivalent is nepheline syenite. Phonolite is typically fine ...
It is a coarse-grained, foliated variety of nepheline syenite, [1] sometimes called nepheline syenite gneiss or gneissic nepeheline syenite. [2] Litchfieldite is composed of two varieties of feldspar (mostly albite but also some microcline), with nepheline, sodalite, cancrinite and calcite.
It is black to dark grey and may appear grey to white in reflected light on polished thin section with reddish brown internal reflections. [5] It has the chemical formula of (Ce,Na,Ca)(Ti,Nb)O 3. [4] Nioboloparite is a variation of loparite-(Ce) containing niobium. [6] Loparite occurs as a primary phase in nepheline syenite intrusions and ...