Zussmanite

zussmanite

stilpnomelane

deerite

grunerite

Images

Formula: K(Fe,Mg,Mn)13(Si,Al)18O42(OH)14
Phyllosilicate
Specific gravity: 3.146
Streak: White
Colour: Light to medium green
Common impurities: Na,Ti
Environments

Metamorphic environments

Zussmanite occurs in stilpnomelane and quartz gneiss (Mindat). It is a mineral of blueschist facies metamorphic rocks (Webmin).

Localities

At Punta Nihue, Cautín Province, Araucanía, Chile, zussmanite occurs in banded stilpnomelane schists. These are intercalated in a complex of low-grade metamorphic rocks with local high-pressure, low-temperature overprint, such as blueschist. The rock contains conspicuous porphyroblasts of zussmanite of mm size and is composed of chemically distinct bands with the subsequent assemblages:
(1) zussmanite, stilpnomelane and quartz
(2) siderite and quartz with or without stilpnomelane
(3) apatite, stilpnomelane, and quartz with or without siderite.
The rarity of rock-forming zussmanite can be explained by its occurrence in strongly iron-rich and reduced rocks, as well as, possibly, by a narrow P-T stability field (MM 62.869-876).

At the type locality, the Laytonville Quarry, Laytonville, Coastal Range, Mendocino county, California, USA, zussmanite occurs as green grains and bands of grains in a black matrix, probably as a result of blueschist facies metamorphism of deep ocean sediments. Associated minerals include deerite, howieite, stilpnomelane, spessartine, riebeckite, crocidolite, quartz, aegirine, grunerite, aragonite, manganese-bearing siderite, ferroan kutnohorite, graphite and pyrite (AM 50.278, Mindat, HOM).

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