Alamosite , Leadhillite , Melanotekite Locality: Tsumeb , Otjikoto (Oshikoto) Region, Namibia ( Locality at mindat.org ) Size: miniature, 3.5 x 2.5 x 1.5 cm Alamosite, Melanotekite, Leadhillite A small piece but truly oustanding for the finely crystallized alamosite on matrix of finely crysatllized leadhillite, and for the richeness and near-record size of the melanotekite! The overall combination is a relative value in that you get three very rare minerals, in excellent crystals, altogether - and in a displayable specimen, no less! — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Leadhillite
A lead sulfate-carbonate associated with anglesite, forming monoclinic crystals that twin into pseudo-hexagonal plates.
Intro adapted from Wikipedia (CC BY-SA).
Leadhillite is an IMA-recognized mineral species in the sulfate class, with the chemical formula Pb₄(SO₄)(CO₃)₂(OH)₂.
It crystallizes in the monoclinic crystal system (space group P2_1/a).
Key properties: Mohs hardness 2.5–3; specific gravity 6.55; Resinous to adamantine, pearly on {001} luster; refractive index 1.96; optically biaxial.
IMA symbol Lhi, grandfathered status — known before the IMA’s founding, named in 1832.
Occurs as an uncommon secondary mineral in the oxidation zone of lead deposits.
It is found associated with Cerussite, anglesite, lanarkite, caledonite, linarite (Leadhills, Scotland); cerussite, caledonite, linarite, diaboleite, boleite, wherryite, paralaurionite.
The name refers to its initially-noted occurrence at Leadhills, Scotland.