Magnussonite

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Formula: Mn²⁺₁₀As³⁺₆O₁₈(OH,Cl)₂
Arsenite containing hydroxyl and/or halogen, manganese-bearing mineral
Crystal System: Isometric
Specific gravity: 4.14 to 4.49 measured, 4.55 calculated
Hardness: 3½ to 4
Streak: White
Colour: Grass green to emerald green
Environments:

Metamorphic environments

Magnussonite occurs in a metamorphosed iron-manganese orebody (Webmin).

Localities

At the type locality, Långban, Filipstad, Värmland, Sweden, magnussonite occurs as fine-grained encrustations in fissures in dolomite impregnated with hausmannite or in fine-grained hematite, associated with trigonite, dixenite, calcite (Mindat, AM 42.581), dolomite, hausmannite, hematite and manganiferous serpentine (HOM).
Magnussonite from Långban - Image

At the Brattfors mine, Sweden, magnussonite is associated with katoptrite, sonolite, hausmannite, manganosite and magnetite (HOM).

At Sterling Hill, New Jersey, USA, magnussonite occurs very rarely in a metamorphosed stratiform zinc orebody, associated with zincite, willemite, franklinite and kraisslite (HOM, AM69.800).
Magnussonite from Sterling Hill - Image

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