Müllerite
Müllerite is an IMA-recognized mineral species in the halide class, with the chemical formula Pb₂Fe³⁺(Te⁶⁺O₆)Cl.
It crystallizes in the hexagonal crystal system (space group P312). It is a member of the Backite structural group.
Key properties: Mohs hardness 2; specific gravity 5.812; Pale yellow streak; Subadamantine to greasy luster.
IMA symbol Mül, IMA status: approved, named in 2019.
A secondary, oxidation-zone mineral presumed to be produced through oxidation of earlier formed tellurides, most likely hessite, with chalcopyrite and galena.
It is found associated with Acanthite, cerussite, hematite, khinite, phosphohedyphane, thorneite, timroseite.
The mineral was named to honor Franz-Joseph Müller, Freiherr von Reichenstein or Franz-Joseph Müller von Reichenstein (1740 or 1742 to 1825 or 1826).