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

Volcanic igneous environments
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).


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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