Protocaseyite
Protocaseyite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula [Al₄(OH)₆(H₂O)₁₂][V₁₀O₂₈]·8H₂O.
It crystallizes in the triclinic crystal system (space group P-1). It is a member of the Pascoite structural group.
Key properties: Mohs hardness 2; specific gravity 2.45; Pale orange-yellow streak; Vitreous luster.
IMA symbol Pcy, IMA status: approved, named in 2021.
Found in a low-temperature, post-mining, underground, secondary mineral assemblage formed on montroseite- and corvusite-bearing sandstone by oxidation in a moist environment.
It is found associated with Ammoniozippeite, gypsum, postite.
The prefix compares this new mineral’s structure to caseyite, which contains sheets of Al3+ linked by µ3-OH bridges (referred to as “flatimers”). The [Al4(OH)6(H2O)12]6+ tetramer in this new phase.