Cerussite

Class: Carbonates (Nitrates)
Group: Aragonite

Common in the oxidised zone of lead deposits, where it may constitute an important ore (Anthony et al., 2001—2005). Faceted specimens are very rare. The largest faceted stone is a 408 carat from Tsumeb, Namibia (Arem, 1987: 64).

Cerussite — specimen 0029, photo © NMNHS

Original description: ‘Cerussit’ Haidinger, W., 1845. Cerussit — Handbuch der Bestimmenden Mineralogie, Braumüller & Seidel, Wien: 503 [view in ‘Library’].

Type locality: Vicenza Province, Veneto, Italy.

Type material: unknown.

Etymology: from the Latin cerussa, meaning ‘white lead’.

Distribution: some of the many localities for fine crystals include: Australia: Tasmania, near Dundas; Germany: Rhineland-Palatinate, near Braubach; Italy: Sardinia, near Iglesias; Namibia: Tsumeb; Russia: Zabaykalsky Krai, Nerchinsk (Anthony et al., 2001—2005).

Chemistry

PbCO3

Essential elements: carbon (C), oxygen (O), lead (Pb).

Crystal data

Crystallography: orthorhombic — dipyramidal. Crystal habit: crystals, to 0.6 m, are tabular {010}, equant to elongated on [001] or [100], or pseudohexagonal dipyramidal {111}, exhibiting combinations of {110}, {010}, {111}, {021}, {012}, {011}, {130}, {001}, with many others. also granular, pulverulent, as randomly intergrown prismatic aggregates, rarely fibrous, massive. Twinning: common, as simple or cyclic contact twins on {110}, producing stellate pseudohexagonal or reticulated composites; as contact twins on {130} producing heart-shaped composites; both laws may occur in one aggregate (Anthony et al., 2001—2005).

Physical properties

Cleavage: on {110} and {021}, good; on {010} and {012}, poor (Anthony et al., 2001—2005). Fracture: conchoidal (Anthony et al., 2001—2005). Tenacity: very brittle (Anthony et al., 2001—2005). Hardness: 3—3.5 (Arem, 1987: 63). Density: 6.46—6.57 g/cm3 (Lazzarelli, 2012). Luminescence: may fluoresce yellow under LW UV (Anthony et al., 2001—2005). Other: soluble in dilute nitric acid with effervescence.

Optical properties

Colour: colourless, white, pale yellow, smoky to dark grey, black with inclusions; colourless in transmitted light (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent (Anthony et al., 2001—2005). Lustre: adamantine, tending toward vitreous, resinous (Anthony et al., 2001—2005). Refractive index: 1.803—2.078 — anisotropic [biaxial (-)] (Lazzarelli, 2012). Birefringence: 0.274. Dispersion: 0.055, greater than diamond (Arem, 1987: 63). Pleochroism: none (Arem, 1987: 63).

Material from ‘Repository’

1 specimen: 0029 — 3.71 ct, Namibia, Oshikoto, Tsumeb.

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