Leadhillite

Leadhillite


Composition: Pb4(SO4)(CO3)2(OH)2
Crystal System : Monoclinic; (ps.Trigonal)
Colours: Colourless, grey, white, pale-yellow
Lustre : Adamantine, resinous
Hardness (H) : 2.5-3.0
Specific Gravity (S.G) : 6.45-6.55

Distribution

Rare. First and second oxidation zones.

Occurrence

  • Supergene
  • 1st Oxidation Zone
  • 2nd Oxidation Zone

Notable Finds

The best crystals, to 130 mm, were found in the second oxidation zone; a 90 mm crystal in the Harvard University collection (Harvard # 107992) is catalogued from 29 Level. However, large crystals were also found in the first oxidation zone as evidenced by specimens in the Karabacek collection at Harvard University, (ref. Harvard # 93920). Currier (2015) describes the purchase of three outstanding leadhillite specimens during a visit to Tsumeb in 1979; a photograph of one of these specimens, now in the MIM Museum, in Beirut, accompanies these notes.

Paragenetic and General Notes

Leadhillite is very much rarer than either anglesite or cerussite, reflecting it's relatively narrow Eh/pH stability range between these two minerals which is also highly dependent on the activity of other dissolved species.

Keller (1977) recognises the following "rare mineral paragenesis": primary sulphides >> wulfenite >> alamosite >> kegelite >> leadhillite >> cerussite.

The following minerals are reported to form pseudomorphs after leadhillite:  cerussite (rare, usually surface alteration only).