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Formula: ◻Ca2(Fe2+3Al2)(Si6Al2)O22(OH)2
Inosilicate (chain silicate),
tschermakite root name group,
calcium amphibole subgroup,
w(OH,F,Cl)-dominant amphibole group,
amphibole supergroup, forms
a series with tschermakite
Crystal system: Monoclinic
Specific gravity: 3.260 calculated
Hardness: 5 to 6
Streak: Dark green
Colour: Dark green
Luminescence: Not fluorescent
Common impurities: Ti,Mn,Na,K,F,Cl,Mg,Fe2+
Environments
Pegmatites
Metamorphic environments
Ferro-tschermakite occurs as a rock-forming mineral in granitic
pegmatites, and also in a variety of metamorphic rocks such
as amphibolite,
metacarbonate,
schist and gneiss.
Associated minerals include plagioclase,
staurolite, almandine,
biotite and chlorite
(HOM).
Localities
At the Bâtiment et Granit de Ploumanac’h northern granite quarry, La Clarté, Perros-Guirec, Ploumanac’h granitic
complex, Brittany, France, the granite is coarse grained and
porphyroid, with a pronounced pink colour due to the presence of
large feldspar crystals. Ferro-tschermakite occurs as ∼3 cm long
aggregates of dark green bladed to acicular crystals associated with white
plagioclase in a granite
pegmatite. Ferro-tschermakite is nonfluorescent and
has a dark green streak and a vitreous lustre
(AM 103.2040).
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