Outstanding brown rounded crystal aggregtes of the rare mineral grantsite from Agios Konstantinos (Lavrion District, Attiki Prefecture, Greece). — Photo: David Hospital · CC BY-SA 4.0
Grantsite
Grantsite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula (Na,Ca)₂₊ₓ(V⁵⁺,V⁴⁺)₆O₁₆·4H₂O.
It crystallizes in the monoclinic crystal system. It is a member of the Hewettite structural group.
Key properties: Olive-green to brownish green streak; Silky or pearly to subadamantine luster; optically biaxial.
IMA symbol Gs, IMA status: approved, named in 1964.
Found in partially oxidized portions of sandstone seams and coalified wood in vanadiferous uranium deposits of the Colorado Plateau type.
It is found associated with Haggite, paramontroseite, corvusite, rauvite, hewettite, carnotite, tyuyamunite.
The name refers to the town of Grants, New Mexico, USA, near which it was first discovered. Type Material: National Museum of Natural History, Washington, D.C., USA, 121956.