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Formula: Ca7Mg(SiO4)4
Nesosilicate (insular SiO4 groups)
Crystal System: Orthorhombic
Specific gravity: 3.42 measured, 3.32 calculated
Streak: White
Colour: Colourless, grey
Solubility: Dissolves readily in the weakest acids, leaving a silica
pseudomorph
Common impurities: Ti,Fe,Mn,Ba,F
Environments
Bredigite occurs in thermally metamorphosed aurioles in intruded
limestone, and in near-surface thermal metamorphism of carbonaceous
limestone
(Dana)).
Localities
At the type locality, Scawt Hill, Larne, County Antrim, Northern Ireland, UK, bredigite occurred in
contact metamorphosed limestone and
dolostone intruded by
dolerite. Associated minerals include
larnite, gehlenite and
spurrite in one assemblage, and
melilite, larnite,
perovskite and magnetite in
another (AM 33.786, HOM). Crystals are squat, barrel or boat shaped, with pseudohexagonal cross sections, or
as slender prismatic crystals, to 2mm long
(Mindat).
At Marble Canyon Mine , Apache Peak area, Culberson county, Texas, USA, bredigite occurs in
syenite monzonite,
associated with larnite
(Dana, HOM).
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