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Formula: NaCa2(Mg4Al)(Si6Al2)O22(OH)2
Inosilicate (chain silicate), amphibole group
Crystal System: Monoclinic
Specific gravity: 3.069 to 3.181
Hardness: 5 to 6
Streak: White
Colour: Green, brown
Common impurities: Ti,Cr,Mn,K,F,H2O,P
Environments:
Pargasite is a common component of skarn metamorphosed from siliceous
limestone. It also may occur in
schist and
amphibolite.
In skarn it is associated with diopside,
phlogopite, corundum,
spinel and calcite.
In metabasalts and andesitic
volcanics the pargasite is associated with
enstatite-ferrosilite,
augite and plagioclase
(HOM).
Localities
Amity, Town of Warwick, Orange county, New York, USA, is an area of
granite intrusions into
marble and associated
gneiss. The marble is
mostly composed of white crystalline calcite that often has small flakes
or spheres of graphite and
phlogopite. Pargasite has been found as shiny black and dark green
crystals to 5 cm in marble
(R&M 96.5.438).
Alteration
magnesium-rich tremolite, tschermakite and
albite to pargasite and
quartz
☐Ca2Mg5Si8O22(OH)2 +
☐Ca2(Mg3Al2)(Si6Al2)O22(OH)2 +
2Na(AlSi3O8) ⇌ 2NaCa2(Mg4Al)(Si6Al2)O22(OH)2 +
8SiO2
(AM 92.4.491)
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