Pectolite

Class: Silicates

Varieties | Names:

A primary mineral in nepheline syenites. A hydrothermal mineral in cavities in basalts and diabases; in serpentinites and peridotites; from metamorphosed calcium rocks (Anthony et al., 2001—2005).

Larimar — specimen 0531, photo © NMNHS

Original description: ‘Pektolith’ von Kobell, F., 1828. Ueber den Pektolith — Archiv für die Gesammte Naturlehre 13: 385—393 [view in ‘Library’].

Type locality: Monzoni, Fassa Valley, Trento Province, Trentino-Alto Adige/Südtirol, Italy; Sano, Mori, Mt Baldo, Lagarina Valley, Trento Province, Trentino-Alto Adige/Südtirol, Italy.

Type material: unknown.

Etymology: from the Greek for compact, in allusion to its resistance to pulverisation.

Distribution: Canada; Germany; India; Italy; Morocco; Russia; South Africa; Sweden; USA (Anthony et al., 2001—2005).

Chemistry

NaCa2Si3O8(OH)

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

Crystal data

Crystallography: triclinic — pinacoidal. Crystal habit: crystals may be tabular, but also commonly acicular, to 15 cm; fine-grained, massive. Twinning: twin axis [010] (Anthony et al., 2001—2005).

Physical properties

Cleavage: perfect on {100} and {001} (Anthony et al., 2001—2005). Fracture: uneven (Anthony et al., 2001—2005). Tenacity: brittle (Anthony et al., 2001—2005). Hardness: 4.5—5 (Anthony et al., 2001—2005). Density: 2.84—2.9 g/cm3 (Anthony et al., 2001—2005). Luminescence: none.

Optical properties

Colour: colourless, whitish, greyish, yellowish; in thin section, colourless (Anthony et al., 2001—2005). Diaphaneity: translucent to opaque (Anthony et al., 2001—2005). Lustre: silky, subvitreous (Anthony et al., 2001—2005). Refractive index: 1.594—1.642 — anisotropic [biaxial (+)] (Anthony et al., 2001—2005). Birefringence: 0.037. Dispersion: weak to very strong (Anthony et al., 2001—2005). Pleochroism: no data.

Material from ‘Repository’

1 specimen: 0531 — 0.39 ct, Dominican Republic.

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