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Sodalite, colorless and transparent in thin section, but frequently pale blue in the hand specimens, is the principal feldspathoid mineral in addition to nepheline. Reddish-brown to black aenigmatite occurs also in these rocks. Extremely iron-rich olivine is rare, but is present in some nepheline syenite
The complex is made up of gabbro and syenite, but more specifically a olivine-plagioclase gabbro and clinopyroxene-plagioclase gabbro. [5] Thin section of gabbro and syenite from the Concord gabbro-syenite complex in plane-polarized light and crossed polarized light.
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.
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 ...
A notable exception where feldspathoids and quartz-bearing rocks are found together is the Red Hill Syenite. [1] Foid, a contraction of the term feldspathoid, is applied to any igneous rock containing up to 60% modal feldspathoid minerals.
Shonkinite is an intrusive igneous rock.More specifically, it is a mafic foidal (feldspathoid bearing) syenite, a holocrystalline (completely crystalline) intrusive rock which, in the restricted sense [clarify], is composed of potassic feldspar (in the form of sanidine), with nepheline, augite, biotite, and olivine. [1]
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In optical mineralogy and petrography, a thin section (or petrographic thin section) is a thin slice of a rock or mineral sample, prepared in a laboratory, for use with a polarizing petrographic microscope, electron microscope and electron microprobe. A thin sliver of rock is cut from the sample with a diamond saw and ground optically flat.