Petalite

Class: Silicates

In granite pegmatites, locally constituting an ore of lithium (Anthony et al., 2001—2005).

Original description: ‘Petalit’ d’Andrada, J. B., 1800. Kurze Angabe der Eigenschaften und Kennzeichen einiger neuen Fossilien aus Schweden und Norwegen, nebst einigen chemischen Bemerkungen über dieselben — Allgemeines Journal der Chemie 4: 36—37 [view in ‘Library’].

Type locality: Utö mines, Utö, Södermanland, Sweden.

Type material: Technische Universität Bergakademie, Freiberg, Germany, 26512 (Anthony et al., 2001—2005).

Etymology: from the Greek for leaf, in allusion to the perfect basal cleavage.

Distribution: Australia; Brazil: Minas Gerais; Canada; Finland; Italy; Namibia: Karibib; Sweden; USA; Zimbabwe (Anthony et al., 2001—2005).

Chemistry

LiAlSi4O10

Essential elements: lithium (Li), oxygen (O), aluminium (Al), silicon (Si).

Crystal data

Crystallography: monoclinic — prismatic. Crystal habit: crystals tabular on {010}, to 2 m; some faces may be striated. Twinning: common on {001}, lamellar (Anthony et al., 2001—2005).

Physical properties

Cleavage: perfect on {001}, poor on {201} (Anthony et al., 2001—2005). Fracture: imperfectly conchoidal (Anthony et al., 2001—2005). Tenacity: brittle (Arem, 1987: 149). Hardness: 6—6.5 (Arem, 1987: 148). Density: 2.4 g/cm3 (Lazzarelli, 2012). Luminescence: none. Other: thermoluminescent (Anthony et al., 2001—2005).

Optical properties

Colour: colourless, white, grey, rarely reddish or greenish; colourless in thin section (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent (Anthony et al., 2001—2005). Lustre: vitreous (Anthony et al., 2001—2005). Refractive index: 1.502—1.523 — anisotropic [biaxial (+)] (Lazzarelli, 2012). Birefringence: 0.012—0.016. Dispersion: 0.0141. Pleochroism: none.

Material from ‘Repository’

4 specimens: 0434 — 1.15 ct, Brazil; 0425 — 0.98 ct, Brazil; 0287 — 4.20 ct, Brazil; 0356 — 1.88 ct, Brazil.

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