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Formula: Zn2(Mn4+,Mn3+)5O10.4H2O
Multiple oxide, manganese-bearing mineral
Crystal System: Monoclinic
Specific gravity: 4.01 measured, 3.983 calculated
Hardness: 4½
Streak: Dark brown
Colour: Dark brown to black
Environments
Metamorphic environments
Hydrothermal environments
Localities
At the Moonshine Mine, Lardeau, Revelstoke Mining Division, British Columbia, Canada, woodruffite occurs in the oxidised zone of a
silver-lead-zinc
ore deposit, associated with smithsonite, gunningite,
hydrozincite and aurichalcite
(HOM).
At the Donimalai Mine, Sandur, Bellary-Hospet iron belt, Ballari District, Karnataka, India, woodruffite occurs in massive
manganese ores, associated with cryptomelane,
lithiophorite, pyrolusite,
ramsdellite, jacobsite,
manganite and braunite
(Dana, HOM).
At the type locality, the Passaic pit, Sterling Hill, Ogdensburg, Franklin Mining District, Sussex County, New Jersey, USA, woodruffite
occurs in the oxidised portion of deeply weathered
manganese-zinc minerals from a
zinc silicate and zinc oxide deposit hosted by
marble. The woodruffite is
found chiefly as masses and crusts with a botryoidal surface and a concentric, coarsely layered internal structure. Occasionally, corroded
crystals of franklinite are found embedded in the masses, and some of the layers may contain
disseminated, platy crystals of chalcophanite;
cryptomelane is another associated mineral
(AM 38.761-769, Mindat).
Alteration
The thermal stability of woodruffite is comparable to that of todorokite, breaking down
at ~300oC and eventually transforming to a spinel-type structure
(AM 88.1697-1701).
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