Formula: Mn2+10As3+6O18(OH,Cl)2
Arsenite containing hydroxyl and/or halogen
Specific gravity: Greater than 4.4
Hardness: 3½ to 4
Streak: White
Colour: Grass reen to emerald green

Metamorphic environments

Magnussonite occurs in a metamorphosed Fe-Mn orebody.
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 , dolomite, hausmannite, hematite and manganiferous serpentine.
At the Brattfors mine, Sweden, magnussonite is associated with katoptrite, sonolite, hausmannite, manganosite and magnetite.
At Sterling Hill, New Jersey, USA, magnussonite occurs very rarely in a metamorphosed stratiform zinc orebody, associated with zincite, willemite, franklinite and kraisslite.

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