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Sodalite thin section

About Sodalite
Sodalite is a feldspathoid mineral, a chloride-containing sodium aluminosilicate that occurs with leucite, nepheline, cancrinite in such igneous rocks as nepheline syenite, trachyte, and phonolite. The name is derived from composition, its contains sodium (soda) (Na).
Sodalite hand-specimen
Formula: Na8Al6Si6O24Cl2
System: Cubic (Isometric)
Color: Any, especially blue to violet
Lustre: Vitreous, Greasy
Hardness: 5½–6
Density: 2.27–2.33
Sodalite #1 thin section (hFOV 2mm)
Sodalite PPL properties
Relief: Moderate negative
Habit/Form: Crystals are dodecahedra, which in thin section show six-sided cross section. Sodalite is often anhedral in plutonic rocks. Symmetrically or zonally arranged inclusions are common in nosean and hauynite. Phenocrysts may be partially resorbed and have embayed edges.
Color: Colorless, gray, pale blue, or pale pink; sometimes color-zoned
Cleavage: Poor on {110}; usually not seen in thin section, more likely to show on edges of the slide.
Sodalite XPL properties
Isotropy/Anisotropy: Isotropic
Interference color: Isotropic (black)
Extinction angle:
Twins: Absent
Uniaxial/Biaxial: Isotropic
Optic axial angle (2V):
Sodalite distinguishing features under the microscope
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  • Deer, W. A., Howie, R. A., & Zussman, J. (2013). An introduction to the rock-forming minerals (pp. 498). Mineralogical Society of Great Britain and Ireland, London.
  • mindat.org – The Mineral Database