Kokinosite

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Formula: Na₂Ca₂(V₁₀O₂₈).24H₂O
Valence: Na₂Ca₂(V⁵⁺₁₀O₂₈).24H₂O
Hydrated decavanadate, pascoite family group
Crystal System: Triclinic
Specific gravity: 2.35 calculated for the empirical formula and 2.352 for the ideal formula
Hardness: 1½
Streak: Yellow
Colour: Yellow-orange to tinted orange-brown
Luminescence: Does not fluoresce in short wave or long wave UV
Environments

Sedimentary environments

Localities

The type locality, the Saint Jude Mine, Slick Rock Mining District, Colorado, USA, is a stope not far from the interconnected West Sunday and Sunday mines. All three mines are currently inactive and their entrances are sealed. Kokinosite is rare; it was found growing on a corvusite - montroseite-bearing sandstone block and is closely associated with gypsum, huemulite, metarossite, pascoite, rossite and wernerbaurite. Other minerals found in the same area in the St. Jude mine include calciodelrioite, delrioite, hendersonite, hughesite, nashite, powellite, postite and schindlerite. Other minerals found nearby in adjacent areas of the West Sunday mine are andersonite, gunterite, hewettite, munirite, natrozippeite, pyrite, rakovanite, sherwoodite and tyuyamunite.
The Kokinosite forms from the oxidation of montroseite - corvusite assemblages in a moist environment. Mining operations have exposed unoxidised and oxidised phases. Under ambient temperatures and generally oxidising near-surface environments, water reacts with pyrite in the deposit to form aqueous solutions with relatively low pH (acid). The various secondary vanadate phases that formed depend upon the ambient conditions and the presence of other cations such as Na¹⁺, Ca²⁺, Mg²⁺ and Al³⁺.
Kokinosite typically occurs as tablets or blades up to 0.05 mm thick, with stepped faces, and 1 mm maximum dimension. Crystals sometimes form larger, irregularly stepped crystal masses up to several mm across. Kokinosite is yellow orange, although it is sometimes tinted orange-brown; the streak is yellow, typical of decavanadate-bearing minerals. The lustre of kokinosite is subadamantine, and the mineral is transparent (CM 52.1.15-25).

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