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Formula:NaFe3+9+x(PO4)6(OH)11.3H2O (x ~ 0.33)
Hydrated phosphate containing hydroxyl
Crystal System: Monoclinic
Specific gravity: 3.04 to 3.3 measured, 3.34 calculated
Hardness: 3
Streak: Yellow
Colour: Greenish yellow, greenish white, yellow, light green
Environments
Pegmatites
Hydrothermal environments
Kidwellite occurs in moderate abundance as a late-stage replacement of earlier phosphate minerals, such as
rockbridgeite and beraunite,
in novaculite deposits. Associated minerals include
rockbridgeite, dufrénite,
beraunite, strengite,
chalcosiderite and goethite;
kidwellite is found rarely in phosphate-rich granite
pegmatites. Dufrénite
or natrodufrénite may overgrow kidwellite in an epitaxial way,
and vice-versa
(AM 64.242, Mindat, HOM).
Localities
At the type locality, Fodderstack Mountain, Norman, Montgomery county, Arkansas, USA, kidwellite is associated with
rockbridgeite, dufrénite,
beraunite and
strengite in phosphate-bearing iron
deposits
(Mindat, Dana).
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