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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
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
kosmochlor–jadeite
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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