Brown crystal aggregates of the very rare chromium mineral guyanaite on a matrix of black eskolaite from the type locality for guyanaite: Merume River, Kamakusa, Mazaruni District, Guyana. — Photo: David Hospital · CC BY-SA 4.0
Guyanaite
A chromium oxyhydroxide intergrown nearly invisibly with the related phases bracewellite, grimaldiite and eskolaite.
Intro adapted from Wikipedia (CC BY-SA).
Guyanaite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula CrO(OH).
It crystallizes in the orthorhombic crystal system (space group P2_1nm).
Key properties: Yellow-brown, greenish brown streak; optically biaxial.
IMA symbol Guy, IMA status: approved, named in 1967.
Found in fine-grained intergrowth with other chromium oxide-hydroxide minerals (Merume River, Guyana); in chromium-rich tremolite skarns, metaquartzites, and chlorite veins (Outokumpu, Finland).
It is found associated with Bracewellite, eskolaite, grimaldiite, mcconnellite (Merume River, Guyana).
The name refers to its occurrence in Guyana.