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Formula: NaCa2(Mg4Fe3+)(Si6Al2)O22(OH)2
Inosilicate (chain silicate),
hastingsite root name group,
amphibole, forms series with
hastingsite and with
pargasite
Crystal System: Monoclinic
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 lots 10 and 11 of concession 1, Bathurst Township, Lanark County, Ontario, Canada (DeWitts corner), the deposit is
located in the Grenville Geological Province, which consists mostly of
marble, gneiss, and
quartzite.
Syenite-migmatite was
also reported in the area where the vein-dikes are located. Characteristic features of the vein-dikes include the
fact that perfectly formed euhedral crystals of different minerals can often be found floating in
calcite with no points of contact with the walls. Sometimes these crystals
have inclusions of calcite, irregular or rounded in shape. It has been argued
that at least some of the vein-dikes were formed as a result of melting of Grenville
marble.
Amphibole-group minerals are abundant in the vein-dikes and are represented
mostly by intermediate members of the magnesio-hastingsite–pargasite
series. They form black equant and short-prismatic crystals to 3 cm that are often severely distorted
(R&M 97.6.556-564).
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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