Laurionite

Crystal System: Orthorhombic
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Lead chloride hydroxide
Chemical Formula: PbClOH
Method(s) of Verification: Eaglebrook (Nantycagl) Mine - XRD (Natural History Museum, London, 9929F).

Geological Context:

  • Supergene: post-mining oxidation & weathering deposits
Introduction: laurionite forms in the oxidized zone of lead-bearing mineral deposits and in lead-bearing slag exposed to saline water.
Occurrence in Wales: an extremely rare Welsh mineral species. Only a couple of specimens containing microcrystals have been recorded, and these are all from a single locality in Central Wales – Eaglebrook Mine.

Key Localities:

  • Eaglebrook (Nantycagl) Mine, Ceulanymaesmawr, Ceredigion: found by Rust et al. (1995) occurring as cleavages to a few square mm in area, on two micro specimens of highly altered galena and dolomite. It was originally mistaken for lanarkite forming, massive colourless to white material with a very slight bluish tint. Where cavities have allowed crystal development, typical forms include thin bladed crystals up to 1 mm in length, and prismatic forms, up to 0.75 mm occur in cavities in oxidized ferroan dolomite. Perfect length parallel cleavage in the crystals and observed flexibility of cleavage flakes is recorded. Partial overgrowth by mattheddleite is noted as a coating of tiny crystals and associated species include anglesite, probable susannite/leadhillite, and caledonite.

References:

  1. Rust, S., Burchmore, S. & Foy, E., 1995. Some interesting new finds from the Nant-y-cagle mine. British Micromount Society Newsletter, 40, 8-10.