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Formula: K(Mn4+7Mn3+)O16
Multiple oxide, coronadite group,
manganese-bearing mineral
Crystal System: Monoclinic
Specific gravity: 4.17 to 4.41 measured, 4.44 calculated
Hardness: 5 to 6½
Streak: Brownish black
Colour: Grey to black (Dana)
Environments:
Pegmatites
Hydrothermal environments
Cryptomelane is the commonest of the hard, black, fine-grained manganese oxides formerly called
psilomelane. It is
a low-temperature(R&M88.3.279) supergene
mineral(JRS 8(1).1-9), widespread in oxidised manganese deposits
as open-space fillings or replacing primary
manganese-bearing
minerals. It is commonly replaced by other secondary
manganese minerals, and associated with
pyrolusite, nsutite,
braunite,
chalcophanite, manganite and
other manganese oxides
(HOM).
At Burdell Gill, Caldbeck Fells, Cumbria, England, there is some evidence that cryptomelane has
pseudomorphed a
rhombohedral mineral, possibly ankerite or
siderite
(JRS8(1).1-9).
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