:Locality: Serra da Mina, Cercal, Evora District, Portugal Class: Crystals on Matrix Size: 5 × 3.5 × 3 cm Description: This is a very rich corkite specimen formed by several extremely brilliant and lustrous crystals, peppering a colorfull goethite matrix. Corkite is an uncommon, low-temperature, secondary mineral occurring in the oxidised zones of hydrothermal base-metal deposits. Really amazing under loupe. — Photo: Joan Rosell , from rosellminerals.com · CC BY-SA 4.0
Corkite
Corkite is a phosphate mineral in the beudantite subgroup of the alunite group. Corkite is the phosphate analogue of beudantite and with it, a complete solid solution range exists. Corkite will also form a solid solution with kintoreite. Corkite is named after County Cork, Ireland; the location where the first notable amount was discovered in 1869. Like many of the other minerals in the beudantite group, corkite is a relatively uncommon, secondary mineral that occurs in oxidation zones near hydrothermal base metal deposits.
Intro adapted from Wikipedia (CC BY-SA).
Corkite is an IMA-recognized mineral species in the phosphate class, with the chemical formula PbFe³⁺₃(SO₄)(PO₄)(OH)₆.
It crystallizes in the hexagonal crystal system (space group R3m). It is a member of the Alunite-beudantite structural group.
Key properties: Mohs hardness 4; specific gravity 4.302; Vitreous to resinous luster; refractive index 1.938; optically uniaxial.
IMA symbol Cok, IMA status: approved, named in 1857.
A rare secondary mineral formed at low temperatures or by weathering in oxidized hydrothermal base-metal deposits.
It is found associated with Pyromorphite, malachite, plumbojarosite, "limonite", quartz.
The name refers to its first-noted occurrence, in Co. Cork, Ireland.