Roymillerite
A colorless transparent lead-molybdate arsenate with a complex structure, found in Namibia's Otavi Valley.
Intro adapted from Wikipedia (CC BY-SA).
Roymillerite is an IMA-recognized mineral species in the silicate class, with the chemical formula Pb₂₄Mg₉(Si₁₀O₂₈)(CO₃)₁₀(BO₃)(SiO₄)(OH)₁₃O₅.
It crystallizes in the triclinic crystal system (space group P-1). It is a member of the Molybdophyllite structural group.
Key properties: Mohs hardness 3; specific gravity 5.973; White streak; Vitreous luster; optically biaxial.
IMA symbol Roy, IMA status: approved, named in 2016.
Found in locally Pb-Cu-rich, non-sulfide portions of an Fe-Mn oxide deposit.
It is found associated with Rhodochrosite, cerussite, jacobsite, hausmannite, sahlinite, barite, grootfonteinite, Mn-Fe oxides, melanotekite.
The mineral was named to honor Dr. Roy McGillivray Miller (b. 1941) for his contributions to the knowledge of the geology of Namibia.