Mereheadite
A rare lead oxychloride found with mendipite in the manganese pods of Merehead quarry, Somerset.
Intro adapted from Wikipedia (CC BY-SA).
Mereheadite is an IMA-recognized mineral species in the borate class, with the chemical formula Pb₄₇O₂₄(OH)₁₃Cl₂₅(BO₃)₂(CO₃).
It crystallizes in the monoclinic crystal system (space group Cm).
Key properties: Mohs hardness 3.5; specific gravity 7.12; White streak; Vitreous to resinous luster.
IMA symbol Mrh, IMA status: approved, named in 1996.
A secondary low-temperature mineral formed in lenses and cavities, in a Mississippi Valley type lead deposit in limestone.
It is found associated with Cerussite, blixite, mendipite (typically intergrown with mereheadite); symesite, rickturnerite, hydrocerussite, parkinsonite, calcite, ‘wad’.
The name refers to the first locality, Merehead Quarry, England.