Deerite

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Formula: Fe²⁺₆Fe³⁺₃(Si₆O₁₇)O₃(OH)₅
Inosilicate (chain silicate), single chains, deerite-howieite group
Crystal system: Monoclinic
Specific gravity: 3.837 measured, 3.86 calculated
Hardness: 6
Streak: Dark grey
Colour: Black
Common impurities: Mg, minor Mn²⁺ may replace Fe²⁺ and minor Al may replace Fe³⁺ (Mindat)
Environments

Metamorphic environments

Localities

At Cervione, Corte, Haute-Corse, Corsica, France, a deerite-bearing rock occurs at the boundary between quartzite and metabasites (fine-grained metamorphic rocks) within the ‘schistes lustrés’ of eastern Corsica. It contains the assemblage pyroxene, blue amphibole, hematite and magnetite. Pyroxene shows homogeneous composition close to the aegirine end-member and blue amphibole is zoned from a crossite (a discontinued amphibole name for a mineral intermediate between the riebeckite group and the glaucophane group) core to a riebeckite rim. The bulk chemical analysis of the rock is remarkable for its very high iron content and the presence of an unusually large amount of Zn which is concentrated in both deerite and amphibole.
P-T conditions of metamorphism, previously estimated to be 8 kbar and 300°C, are in good agreement with present knowledge of the deerite stability field (Journal of Metamorphic Geology 4.4.385-399).

At the type locality, the Laytonville Quarry, Laytonville, Coastal Range, Mendocino County, California, USA, deerite occurs in blueschist facies metasediments formed at high pressure and low temperature. Associated minerals include howieite, zussmanite, stilpnomelane, spessartine, riebeckite, quartz, aegirine, grunerite, aragonite, manganese-bearing siderite and Fe²⁺-bearing kutnohorite (HOM).
Deerite from the Laytonville Quarrry - Image

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