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Formula: (Ca,Mn2+)0.2(Mn4+,Mn3+)O2.0.6H2O
Multiple oxide, manganese-bearing mineral
Crystal System: Trigonal
Specific gravity: 3.20 measured
Hardness: 2½ to 3
Streak: Dark brown
Colour: Black, brownish, violet
Environments:
Localities
At the type locality, Rancié, Occitanie, ranciéite occurs in cavities in
limonite
(Dana).
At the Filhols Mine, Romano, Italy, ranciéite occurs in lake-deposited tuff, associated with
halloysite
(Dana).
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