Information about Descloizite

Descloizite is a secondary lead zinc vanadate mineral forming in the oxidised zones of lead-zinc ore deposits, most prized by collectors for its lustrous, often gem-quality crystals in rich chocolate-brown, orange-brown, reddish-brown, or near-black.

The finest descloizite specimens come from Namibia – particularly from the Berg Aukas, Abenab West, and other mines in the Grootfontein district, which have produced prismatic to tabular crystals of exceptional quality in brilliant deep reddish-brown to blackish colour, sometimes combined on matrix with other secondary vanadate minerals such as vanadinite and wulfenite. These Namibian specimens are among the most coveted of all vanadate minerals. Additional notable localities include the Sierra de Córdoba in Argentina, Tsumeb in Namibia, and various Arizona copper districts.

The name honours the French mineralogist Alfred Louis Olivier Legrand Des Cloizeaux (1817–1897), a distinguished crystallographer who made important contributions to optical mineralogy and the measurement of crystal optical properties.

Uses and History

Descloizite was first described in 1854 by the French mineralogist Augustin Alexis Damour from specimens from Córdoba, Argentina. Des Cloizeaux, in whose honour it was named, was at the time one of Europe’s foremost mineralogical crystallographers and had contributed work on the optical measurement of minerals that was fundamental to the development of modern optical mineralogy.

Descloizite is occasionally associated with vanadium ore deposits of economic significance; vanadium, extracted largely from its ores as vanadium pentoxide, is an important steel-strengthening alloy additive, and secondary vanadate minerals including descloizite can represent concentrations of vanadium in oxidised lead-zinc deposits. However, it is collected primarily as a specimen mineral.

In Wales, descloizite has been recorded from the oxidised zones of certain lead-zinc veins in the Central Wales Orefield, where vanadate mineralisation occurs in association with galena-sphalerite-bearing vein systems. Material is typically small-scale and of limited collecting significance compared to Namibian specimens.

Mineralogy

Hazards and Warnings

Toxic mineral: contains lead and vanadium. Lead is a serious cumulative toxin. Vanadium compounds are also toxic. Wash hands thoroughly after handling, avoid inhaling dust, and keep away from children and food preparation areas.

Almost all rocks, minerals (and, frankly, almost all other substances on earth) can produce toxic dust when cutting, which can cause serious respiratory conditions including silicosis. When cutting or polishing rocks, minerals, shells, etc, all work should be done wet to minimise the dust, and a suitable respirator or extraction system should be used.

Translations

Further Reading / External Links

• https://en.wikipedia.org/wiki/Descloizite
• https://www.mindat.org/min-1249.html
• https://www.handbookofmineralogy.org/pdfs/descloizite.pdf