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Formula: ☐Na2(Fe2+3Al2)Si8O22(OH)2
Inosilicate (chain silicate), forms a series with glaucophane
Crystal System: Monoclinic
Specific gravity: 3.224 calculated
Hardness: 5 to 6
Streak: Pale grey to bluish grey
Colour: Grey to lavender-blue
Common impurities: Ti,Mn,Ca,K
Environments
Ferro-glaucophane occurs in metamorphic rocks of the high-pressure, low-temperature
blueschist facies, commonly derived from either
siliceous sedimentary,
alkalic basaltic, or felsic volcanic predecessors. Associated minerals
include
paragonite, lawsonite,
albite, spessartine,
almandine, epidote and
omphacite
(HOM).
Localities
The type Locality is the Herin mine, Champdepraz, Aosta Valley, Italy.
Ferro-glaucophane from the Herin Mine -
Image
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