Bronze colored crystals of the rare calcium vanadium oxide metahewettite from one of most famous localities for the mineral: Cactus Rat Mine, Grand County, Utah, United States of America. — Photo: David Hospital · CC BY-SA 4.0
Metahewettite
Metahewettite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula CaV⁵⁺₆O₁₆·3H₂O.
It crystallizes in the monoclinic crystal system (space group P2_1/m). It is a member of the Hewettite structural group.
Key properties: specific gravity 2.94; Maroon to brownish red streak; Dull to somewhat silky luster; optically biaxial.
IMA symbol Mhew, grandfathered status — known before the IMA’s founding, named in 1914.
Occurs as an impregnation in sandstone (Colorado Plateau-type U–V deposits).
It is found associated with Hewettite, gypsum, selenium.
The name refers to its relation to hewettite and its lesser H2O content.