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Formula: Ca2Mn2+Al2(Si2O7)(SiO4)
(OH,O)2.H2O
Sorosilicate (Si2O7 groups),
pumpellyite subgroup of
the pumpellyite group,
manganese-bearing mineral
Crystal System: Monoclinic
Specific gravity: 3.34 calculated
Hardness: 5
Streak: Light greyish pink
Colour: Pale grey, pink-brown
Environments
Localities
At the type locality, the Ochiai mine, Kohsai, Minami-Alps City, Yamanashi Prefecture, Japan,
pumpellyite-(Mn2+) occurs as aggregates composed of minute platelets or of very fine granules in
massive braunite ore in a bedded
manganese deposit developed in low-grade metamorphic rocks. Associated
minerals include braunite,
piemontite, clinozoisite,
caryopilite, johannsenite,
rhodochrosite, albite,
quartz and calcite
(HOM, Mindat, AM 68.1250).
The Central Mine, Central, Keweenaw county, Michigan, USA, initially targeted a series of sub-parallel mineralised
fissure veins where the most copper-rich portion of the vein was close to the
base of the main greenstone flow.
Examination of mineralised conglomerate ore from the Central mine dumps resulted in the discovery of brown to tan
prismatic microcrystals of pumpellyite-(Mn2+), associated with beautiful black microcrystals of
manganite, both to around 2 mm
(MinRec 54.1.79).
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