What is Leadhillite?
Leadhillite is a very dense lead sulfate carbonate with curved or tabular crystals from oxidised lead deposits and a distinctive high-lustre surface.
Mineralogy and crystal structure
Reference formula: Pb4SO4(CO3)2(OH)2. Leadhillite is a monoclinic lead sulfate carbonate hydroxide with strong pseudo-hexagonal relationships to related lead minerals. Its high density and softness reflect the lead-rich chemistry; crystal form and associated minerals are important for identification. Leadhillite is classified with carbonates and has a monoclinic crystal system. Typical hardness is 2.5–3 on the Mohs scale and specific gravity is approximately 6.4–6.6.
Colour, lustre and habit
Typical colours include colourless, white, yellow, grey. The usual tabular, curved, granular habit and adamantine, vitreous, pearly lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Leadhillite forms in or is associated with supergene oxidation zones of lead sulfide deposits, commonly with cerussite and anglesite. Important documented localities include Scotland, Namibia, Mexico, the United States, Australia and Germany.
High lustre and unusual geometry in a lead mineral
Leadhillite makes a sophisticated display specimen: pale curved plates can show an almost glassy or adamantine sheen while carrying the chemistry of a weathered galena vein. It is most convincing beside anglesite, cerussite or other secondary lead minerals.
Collecting and care
Lead-bearing and soft: keep enclosed, avoid dust and acids, do not cut or polish, and wash hands after handling.
