Dark green, almost black crystal group of the rare mineral bobfergusonite from Argentina (Nancy Pegmatite, Chacabuco Department, San Luis Province, Argentina). Ex. Erich Laskowski collection (USA). — Photo: David Hospital · CC BY 4.0
Bobfergusonite
A green- to red-brown sodium-manganese-iron phosphate discovered in Manitoba in 1986, named for University of Manitoba professor Robert Ferguson.
Intro adapted from Wikipedia (CC BY-SA).
Bobfergusonite is an IMA-recognized mineral species in the phosphate class, with the chemical formula Na₂Mn²⁺₅Fe³⁺Al(PO₄)₆.
It crystallizes in the monoclinic crystal system (space group P2_1/n). It is a member of the Alluaudite-Wyllieite structural group.
Key properties: Mohs hardness 4; Yellow-brown streak; Resinous, bronzy on parting planes luster; refractive index 1.565; optically biaxial.
IMA symbol Bfg, IMA status: approved, named in 1984.
Occurs as an uncommon primary mineral in the intermediate zone of a granite pegmatite enriched in manganese and fluorine.
It is found associated with Beusite, fillowite, triplite, apatite, alluaudite.
The mineral was named to honor Emeritus Professor Robert Bury Ferguson (1920-), Canadian mineralogist, University of Manitoba, Winnipeg, Canada.