Howieite

howieite

deerite

zussmanite

stilpnomelane

Images

Formula: Na(Fe²⁺,Fe³⁺,Al,Mg)₁₂(Si₆O₁₇)₂(O,OH)₁₀
Inosilicate (chain silicate), deerite-howieite group
Crystal System: Triclinic
Specific gravity: 3.378 measured, 3.34 calculated
Streak: Greyish black
Colour: Dark green to black
Common impurities: Ca,Mg,Ti
Environments

Metamorphic environments

Howieite occurs as bladed crystals in blueschist metamorphic facies (Dana).

Localities

At the type locality, the laytonville Quarry, Laytonville, Coastal Range, Mendocino county, California, USA, howieite is an essential mineral in some of the metamorphosed shales, siliceous ironstones and impure limestones. Associated minerals include deerite, zussmanite, stilpnomelane, spessartine, riebeckite, quartz, aegirine, grunerite, aragonite, manganese-bearing siderite and iron-bearing kutnohorite (HOM).

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