Grass green microcrystals of favreauite, an extremely rare mineral (IMA 2014-013) discovered at the El Dragon mine, Potosí, Bolivia. Favreauite is a selenite of formula PbBiCu6O4(SeO3)4(OH)·H2O. Only one locality known worldwide. Favreauite is the rarest of all selenites found at El Dragon. Very limited finding with a few specimens. Associated minerals are minoritary pink ahlfeldite and blue chalcomenite. — Photo: David Hospital · CC BY-SA 4.0
Favreauite
Favreauite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula PbBiCu₆O₄(SeO₃)₄(OH)·H₂O.
It crystallizes in the tetragonal crystal system (space group P4/n).
Key properties: Mohs hardness 3; specific gravity 4.851; Vitreous luster; optically uniaxial.
IMA symbol Fav, IMA status: approved, named in 2014.
Forms secondarily through oxidation of a selenide-bearing hydrothermal vein hosted by sandstones and shales.
It is found associated with Ahlfeldite, allophane, calcite, chalcomenite, malachite, molybdomenite, alfredopetrovite.
The mineral was named to honor Georges Favreau, amateur mineralogist and professional engineer.