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Formula: K(Fe,Mg,Mn)13(Si,Al)18O42(OH)14
Phyllosilicate
Crystal System: Trigonal
Specific gravity: 3.146 measured, 3.14 calculated
Streak: White
Colour: Light to medium green
Common impurities: Na,Ti
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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