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Class: Silicates
Group: Sodalite

Varieties | Names:

Formed in nepheline syenites and related rock types; in metasomatised calcareous rocks, and in cavities in ejected volcanic blocks (Anthony et al., 2001—2005).

Original description: Thomson, T., 1811. A Chemical Analysis of Sodalite, a new Mineral from Greenland — Journal of Natural Philosophy, Chemistry and the Arts 29: 285—292 [view in ‘Library’].

Type locality: Ilimaussaq, Narsaq, Kitaa, Greenland.

Type material: unknown.

Etymology: the name reflects its sodium content.

Distribution: Bolivia: Cochabamba; Canada; Germany: Eifel district; Italy: at Vesuvius, Monte Somma, Campania; Norway; Russia: Kola Peninsula (Anthony et al., 2001—2005).



Essential elements: oxygen (O), sodium (Na), aluminium (Al), silicon (Si), chlorine (Cl).

Crystal data

Crystallography: isometric — hextetrahedral. Crystal habit: crystals rare, typically dodecahedra, to 10 cm; as embedded grains or massive. Twinning: on {111}, common, forming pseudohexagonal prisms by elongation along [111] (Anthony et al., 2001—2005).

Physical properties

Cleavage: {110}, poor (Anthony et al., 2001—2005). Fracture: uneven to conchoidal (Arem, 1987: 174). Tenacity: brittle (Arem, 1987: 174). Hardness: 5—6 (Lazzarelli, 2012). Density: 2.15—2.4 g/cm3 (Lazzarelli, 2012). Luminescence: bright red-orange cathodoluminescence and fluorescence under LW and SW UV, with yellowish phosphorescence (Anthony et al., 2001—2005).

Optical properties

Colour: colourless, white, yellowish, greenish, light to dark blue, reddish; in thin section, colourless to grеy (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent (Anthony et al., 2001—2005). Lustre: vitreous to greasy (Arem, 1987: 174). Refractive index: 1.478—1.488 — isotropic (Lazzarelli, 2012). Dispersion: 0.018. Pleochroism: none.

Material from ‘Repository’

1 specimen: 0061 — 1.59 ct, Afghanistan.

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