Lazulite

Class: Phosphates, arsenates, vanadates
Group: Lazulite

Disseminated in metamorphic quartzites, schists and quartz veins; in the border zones of complex granite pegmatites (Anthony et al., 2001—2005). Faceted specimens are very rare.

Lazulite — specimen 0066, photo © NMNHS

Original description: ‘Lazulit’ Klaproth, M. H., 1795. Prüfung eines smalteblauen Fossils, von Vorau — Beiträge zur Chemischen Kenntniss der Mineralkörper 1: 197—202 [view in ‘Library’].

Type locality: Freßnitzgraben, Krieglach, Fischbacher Alpen, Styria, Austria.

Type material: Natural History Museum, London, England, 83304 (Anthony et al., 2001—2005).

Etymology: from the Arabic word meaning ‘heaven’, for its colour.

Distribution: Austria: Salzburg, near Werfen, Färbergraben and Höllgraben; Brazil: Minas Gerais; Madagascar; Pakistan: fine crystals from the Chilas area, near Nanga Parbat Peak; USA: California, Mono Co., White Mountains, at the Champion mine (Anthony et al., 2001—2005).

Chemistry

(Mg,Fe2+)Al2(PO4)2(OH)2

Essential elements: hydrogen (H), oxygen (O), magnesium (Mg), aluminium (Al), phosphorus (P), iron (Fe).

Crystal data

Crystallography: monoclinic — prismatic. Crystal habit: as crystals, stubby to acute dipyramidal, to 15 cm, or tabular on {111} or {101}, with several other forms noted; granular, massive. Twinning: common on {100} with composition plane {001}, occasionally producing lamellar or polysynthetic groups; rare on {223}; by reflection on {221} with composition plane {331}; several other twin laws reported (Anthony et al., 2001—2005).

Physical properties

Cleavage: poor to good on {110}; indistinct on {101} (Anthony et al., 2001—2005). Fracture: uneven to splintery (Anthony et al., 2001—2005). Tenacity: brittle (Arem, 1987: 123). Hardness: 5.5—6 (Arem, 1987: 123). Density: 3.04—3.17 g/cm3 (Lazzarelli, 2012). Luminescence: none (Arem, 1987: 123).

Optical properties

Colour: azure-blue, sky-blue, bluish white, yellow-green, blue-green, rarely green (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent; may be nearly opaque (Anthony et al., 2001—2005). Lustre: vitreous (Anthony et al., 2001—2005). Refractive index: 1.604—1.646 — anisotropic [biaxial (-)] (Lazzarelli, 2012). Birefringence: 0.031—0.036. Dispersion: 0.014 (low). Pleochroism: strong; X = colourless; Y = blue; Z = darker blue (Anthony et al., 2001—2005).

Material from ‘Repository’

1 specimen: 0066 — 0.08 ct, Pakistan.

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