Leucite

Class: Silicates
Group: Zeolite

In potassium-rich mafic and ultramafic lavas (Anthony et al., 2001—2005). Faceted specimens are extremely rare.

Original description: ‘Leucit’ Blumenbachs, J. F., 1791. Auszuge und Kezensioneit bergmanischer und mineralogischer Schriften — Bergmannisches Journal 2: 489 [view in ‘Library’].

Type locality: Monte Somma, Somma-Vesuvius Complex, Naples Province, Campania, Italy.

Type material: unknown.

Etymology: from the Greek word λευκός (leucos) for white, in allusion to its colour.

Distribution: Democratic Republic of the Congo; Germany: Eifel district; Italy: at Vesuvius, Monte Somma, Campania; Tanzania: on Kilimanjaro; Uganda: Ruwenzori; USA: at Magnet Cove, Hot Spring Co., Arkansas (Anthony et al., 2001—2005).

Chemistry

KAlSi2O6

Essential elements: oxygen (O), aluminium (Al), silicon (Si), potassium (K).

Crystal data

Crystallography: tetragonal — dipyramidal. Crystal habit: commonly euhedral, pseudocubic crystals, to 9 cm; rarely granular, massive. Twinning: common and repeated on {110}, {101} (Anthony et al., 2001—2005).

Physical properties

Cleavage: very poor on {110} (Anthony et al., 2001—2005). Fracture: conchoidal (Arem, 1987: 125). Tenacity: brittle (Arem, 1987: 125). Hardness: 5.5—6 (Arem, 1987: 125). Density: 2.45—2.5 g/cm3 (Lazzarelli, 2012). Luminescence: none. Radioactivity: GRapi 255.81.

Optical properties

Colour: white, grey; 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: 1.501—1.51 — anisotropic [uniaxial (+)] (Lazzarelli, 2012). Birefringence: 0.01. Dispersion: none. Pleochroism: none.

Material from ‘Repository’

1 specimen: 0064 — 0.05 ct, Italy.

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