Pargasite

Class: Silicates
Group: Amphibole

In skarns metamorphosed from siliceous limestones; schists and amphibolites; also from andesitic volcanic and altered ultramafic rocks (Anthony et al., 2001—2005). Extremely rare as faceted specimens.

Pargasite — specimen 0669, photo © NMNHS

Original description: ‘Pargasit’ Pansner, J. H. L., 1815. Korrespondenz — Taschenbuch für die gesammte Mineralogie mit Hinsicht auf die neuesten Entdeckungen 9: 302 [view in ‘Library’].

Type locality: Pargas, Southwest Finland Region, Finland.

Type material: unknown.

Etymology: after the type locality, Pargas, Finland.

Distribution: rarely in good crystals: Austria: Saualpe, Carinthia; Finland: Pargas; Italy: at Vesuvius, Campania; Pakistan: from Aliabad, Hunza Valley; Sweden (Anthony et al., 2001—2005).

Chemistry

NaCa2(Mg4Al)Si6Al2O22(OH)2

Essential elements: hydrogen (H), oxygen (O), sodium (Na), magnesium (Mg), aluminium (Al), silicon (Si), calcium (Ca).

Crystal data

Crystallography: monoclinic — prismatic. Crystal habit: as stout prismatic crystals, to 3 cm; granular. Twinning: simple or multiple twinning {100}, common (Anthony et al., 2001—2005).

Physical properties

Cleavage: perfect on {110}; partings on {100}, {001} (Anthony et al., 2001—2005). Fracture: no data. Tenacity: brittle (Anthony et al., 2001—2005). Hardness: 5—6 (Arem, 1987: 144). Density: 3.04—3.26 g/cm3 (Lazzarelli, 2012). Luminescence: none (Arem, 1987: 144).

Optical properties

Colour: bluish green, greyish black, light brown, bright green; in thin section, very light brown, bluish green (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent (Anthony et al., 2001—2005). Lustre: vitreous (Arem, 1987: 144). Refractive index: 1.613—1.663 — anisotropic [biaxial (+)] (Lazzarelli, 2012). Birefringence: 0.02—0.024. Dispersion: no data. Pleochroism: X = colourless, greenish yellow; Y = light brown, bluish green, green; Z = light brown, bluish green (Anthony et al., 2001—2005).

Material from ‘Repository’

3 specimens: 0275 — 0.82 ct, Tanzania; 0294 — 0.70 ct, Tanzania; 0669 — 0.60 ct, Tanzania.

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