Magnesio-hastingsite

magnesio-hastingsite

geikielite

spinel

pargasite

Images

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-hastingsitepargasite 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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