Gunterite

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Formula: Na₄Ca(V₁₀O₂₈).20H₂O
Hydrated decavanadate
Crystal System: Monoclinic
Specific gravity: 2.398 calculated for the empirical formula, and 2.400 calculated for the structural formula
Hardness: 1
Streak: Yellow
Colour: Orange-yellow
Luminescence: Not fluorescent under short wave or long wave UV
Solubility: Soluble in water at room temperature
Environments

Sedimentary environments

Gunterite is a relatively new mineral, approved in 2011 and to date (July 2024) reported only from the Slick Rock Mining District (3 different mines).

Localities

At the type locality, the West Sunday Mine, Slick Rock Mining District, San Miguel County, Colorado, USA, gunterite occurs in efflorescences on the sandstone walls of the mine workings and in fractures in the sandstone. The crystals grow both as crystalline crusts on an amorphous dehydrated vanadium phase and as crystals tightly adhered to a corvusite – montroseite matrix. On one of the cotype specimens, crystals of gunterite occur on and with well-formed huemulite crystals. On the other cotype specimen, well-formed crystals of rossite occur on the gunterite crystals. Other minerals found nearby include calcite, hewettite, hughesite, munirite, paramontroseite, pascoite, sherwoodite and rakovanite.
The gunterite is formed from the oxidation of corvusite – montroseite assemblages (CM 49.1243-1251).

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