Bicapite

Images

Formula: [KNa₂Mg₂(H₂O)₂₅][H₂PV⁵⁺₁₂O₄₀(V⁵⁺O)₂]
Polyoxometalate, vanadium-bearing mineral. A polyoxometalate has a polyatomic ion, usually an anion, that consists of three or more transition metal oxyanions linked together by shared oxygen atoms to form closed 3-dimensional frameworks (Wiki).
Crystal system: Tetragonal
Specific gravity: 2.44 measured
Hardness: 1½
Streak: Orange
Colour: Dark red-brown, often appearing black
Solubility: Dissolves slowly in dilute hydrochloric acid
Environments

Sedimentary environments
Hydrothermal environments

Bicapite is a relatively new mineral, approved in 2018 and to date (May 2026) reported only from the type locality

Localities

At the type locality, the Pickett Corral Mine, Montrose County, Colorado, USA, bicapite occurs as square tablets up to about 0.2 mm on edge on montroseite-corvusite-bearing sandstone, formed by oxidation in a moist environment. Crystals are dark red-brown, often appearing black. Associated minerals include gypsum, huemulite, thenardite, montroseite and corvusite.
The name bicapite is in recognition of this being the only known mineral with a structure based on a bicapped Keggin anion. The discovery of bicapite and numerous other natural polyoxometalate compounds in the Colorado Plateau uranium-vanadium deposits make that the most productive region found to date for naturally occurring polyoxometalate compounds (AM 104.12.1851-1856, HOM).
Bicaite from the Pickett Corral Mine - Image

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