An extremely rare black grain of an intergrown mixture of grimaldiite and mcconnellite from the type locality for both species: Merume River, Kamakusa, Potaro-Siparuni Region, Guyana. Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY 4.0
Mcconnellite
Mcconnellite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula Cu¹⁺CrO₂.
It crystallizes in the hexagonal crystal system (space group R3m).
Key properties: specific gravity 5.49.
IMA symbol Mcn, IMA status: approved, named in 1967.
Found in fine-grained intergrowth with other chromium oxide-hydroxide minerals in alluvial cobbles.
It is found associated with Bracewellite, eskolaite, grimaldiite, guyanaite.
The name refers to Dr. Richard Bradford McConnell, formerly Director, British Guyana Geological Survey.