Woodruffite

minerals

franklinite

chalcophanite

cryptomelane

Images
Formula: Zn2(Mn4+,Mn3+)5O10.4H2O
Multiple oxide, manganese-bearing mineral
Specific gravity: 4.01
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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