Johannsenite - Encyclopedia

    Class : Silicates
    Subclass : Inosilicates
    Crystal system : Monoclinic
    Chemistry : CaMnSi₂O₆
    Rarity : Quite common

Johannsenite is a manganese clinopyroxene which forms two series, with diopside on the one hand and with hedenbergite on the other. It is found in limestones which have undergone contact metamorphism with metasomatosis and which are therefore transformed into skarns. It accompanies other manganese silicates (bustamite, rhodonite) and frequent sulphides. It was named in honor of Albert Johannsen, American petrographer and geologist, Professor at the University of Chicago. Johannsenite forms fibrous crystals which are usually grouped into fibroradiated spherolites or radiated aggregates ; they can reach 10 cm. Their green-black or brown color is often blackened by a film of manganese oxides. Johannsenite also alters to rhodonite. It is a locally important manganese ore and it is occasionnally cut in cabochons.

Main photo : Johannsenite and sphalerite from Iron Cap Mine, Arizona, USA © Lawrence Violett

No twins known for this mineral species.

No fakes recorded for this mineral species.