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Formula: NaCa2(Mg4Fe3+)(Si6Al2)O22(OH)2
Inosilicate (chain silicate), hastingsite group, forms series with
hastingsite and with pargasite
Specific gravity: 3.225
Hardness: 5 to 6
Streak: Pale grey-green to pale brownish green
Colour: Green to brownish-green
Common impurities: Ti,Mn,K,H2O
Environments
Volcanic igneous environments
Carbonatites
Metamorphic environments
Magnesio-hastingsite occurs in alkalic basalts, in
andesites, latites,
and tephrites, and their
tuffs; it also occurs in
carbonatites.
Associated minerals include olivine,
plagioclase and pyroxenes
(HOM).
Localities
At the type locality, the Canadian National Railway tunnel, Mont Royal, Montréal, Quebec, Canada,
magnesio-hastingsite occurs in essexite
(AM 13.287-296).
At the Långban mine, Långban Ore District, Bergslagen mining district, Sweden, both plumbian and normal varieties
of magnesio-hastingsite occur in skarn
At the Iron Mountain mine, Fremont county, Colorado, USA, magnesio-hastingsite occurs in metamorphic rock
(AM 13.287-296).
At the Rhein Property, Amity, Town of Warwick, Orange county, New York, USA, magnesio-hastingsite occurs as
well-formed brown to black crystals with a distinctive wedge-shaped cross-section. Crystals to 10 cm have been found.
In 2013, Rhein unearthed world-class examples that were associated with dark red
spinel and occasionally with
geikielite crystals. Graphite is
present on some of the crystal faces
(R&M 96.5.437-438).
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