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Formula: CaSr(Al2Mn3+)[Si2O7]{SiO4]O(OH)
Sorosilicate (Si2O7 groups), epidote group,
strontium- and manganese-
bearing mineral
Crystal System: Monoclinic
Specific gravity: 3.65 to 3.71 measured, 3.73 calculated
Hardness: 6
Streak: Purplish brown
Colour: Dark red
Common impurities: Fe,Ti,Mg,H2O
Environments
Localities
There are two co-type localities, the Cassagna Mine and the Molinello Mine, both at Ne, Genoa, Liguria, Italy. The
manganese mineralisation is associated with a
chert formation overlying
ophiolitic rocks. The complex mineral association can be ascribed to
low-temperature metamorphic conditions of the
prehnite-pumpellyite facies. In addition
to braunite, a wide variety of uncommon mineral species is present.
The piemontite-(Sr) appears generally as small prismatic crystals in veinlets about 3—4 mm thick, which cut a
black manganese ore deposit made up mainly of
quartz and braunite. The veinlets
also contain calcite, rhodonite,
rhodochrosite and
ganophyllite
(EJM 2.519-523).
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