Formula: Mn2+Fe3+2(PO4)2(OH)2.8H2O
Hydrated phosphate containing hydroxyl, manganese mineral
Specific gravity: 2.94
Hardness: 3
Streak: White
Colour: Yellow to brownish yellow


Stewartite occurs in granitic pegmatites. It is a rare, low temperature, oxidation product formed where triphylite has suffered retrograde alkali-leaching, oxidation and hydration. It is associated with lithiophilite, triphylite, hureaulite, strunzite, laueite, pseudolaueite, eosphorite, rockbridgeite, strengite, diadochite, phosphosiderite and iron-manganese oxides (AM 59.1272-1276, HOM).

At the type Locality, the Stewart Mine, Tourmaline Queen Mountain, Pala Mining District, San Diego county, California, USA, stewartite occurs in a pegmatite associated with phosphosiderite, lithiophilite, jahnsite-(MnMnMn) and hureaulite (Mindat, Dana).

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