Black crystal aggregates of the rare iron silicate mineral wilkinsonite from the type locality in Australia (Warrumbungle Volcano, Gowen County, New South Wales) and only one of the three known localities worldwide. — Photo: David Hospital · CC BY-SA 4.0
Wilkinsonite
Wilkinsonite is an IMA-recognized mineral species in the silicate class, with the chemical formula Na₄[Fe²⁺₈Fe³⁺₄]O₄[Si₁₂O₃₆].
It crystallizes in the triclinic crystal system (space group P-1). It is a member of the Sapphirine structural group.
Key properties: Mohs hardness 5; specific gravity 3.89; Brown streak; Vitreous luster; optically biaxial.
IMA symbol Wkn, IMA status: approved, named in 1988.
Found in an eruptive peralkaline trachyte (Warrumbungle volcano, Australia); in syenite ejecta (Wonchi volcano, Ethiopia).
It is found associated with Anorthoclase, sodalite, clinopyroxenes, nepheline, analcime, arfvedsonite, eudialyte (Warrumbungle volcano, Australia); riebeckite, biotite, aegirine.
The name refers to John Frederick George Wilkinson, Emeritus Professor of Geology, University of New England, Armidale, Australia.