Magnesio-arfvedsonite

magnesio-arfvedsonite

braunite

winchite

cummingtonite

Images

Formula: NaNa2(Mg4Fe3+)Si8O22(OH)2
Inosilicate (chain silicate) with double chains, arfvedsonite root name group, sodium amphibole subgroup, w(OH, F, Cl)-dominant amphibole group, amphibole supergroup
Crystal System: Monoclinic
Specific gravity: ~ 3.1 to 3.3 measured, 3.25 calculated
Hardness: 5 to 6
Streak: Pale grey to dark bluish grey
Colour: Bluish black to black, purple
Environments

Pegmatites
Carbonatites

Magnesio-arfvedsonite occurs: as exsolution lamellae in cummingtonite from metamorphosed iron formation; in felsic pegmatites; from sodium metasomatism (fenitisation) around some carbonatites; as authigenic or diagenetic overgrowths on detrital igneous hornblende. Associated minerals include aegirine, braunite, winchite, cummingtonite, albite and biotite (HOM).

Localities

At the type locality, the Hpakant-Tawmaw Jade Tract, Hpakant Township, Mohnyin District, Kachin State, Myanmar, magnesio-arfvedsonite is associated with kosmochlorjadeite solid-solution pyroxene and clinochlore (MM 79.2.253-260).

At the Lepkhe-Nel'm Mountain, Seidozero Lake, Lovozersky District, Murmansk Oblast, Russia, magnesio-arfvedsonite has been found with apatite (FM 85188).
Magnesio-arfvedsonite from the Lepkhe-Nel'm Mountain - Image

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