Formula: Fe3+(PO4).2H2O
Hydrated normal phosphate, variscite group, dimorph of phosphosiderite, forms a series with variscite.
Specific gravity: 2.84 to 2.87
Hardness: 3½ to 4
Streak: White
Colour: Purple, violet, pink, peach-blossom-red, carmine, greenish white, colourless; Colourless to pale pink in transmitted light.
Solubility: Soluble in hydrochloric acid but not in nitric acid.

Sedimentary environments

Strengite is a late secondary mineral in complex granite pegmatites, in iron ores and gossans, with magnetite iron ores and rarely as a cave mineral (HOM). In pegmatites it is a surface product formed by alteration of iron-bearing phosphates such as triphylite or dufrénite (Dana).
Associated minerals include beraunite, hureaulite, dufrénite, bermanite, stewartite, cacoxenite, frondelite/rockbridgeite, vivianite, apatite, limonite, leucophosphite and phosphosiderite (HOM, Dana, Mindat).

At the type locality, the Eleonore Mine, Rodheim-Bieber, Hesse, Germany, strengite occurs in a phosphate-bearing iron ore deposit (Mindat).

At Broken Hill, New South Wales, Australia, strengite is found at Kintore with corkite - hinsdalite and pyromorphite, and globules of strengite/variscite occur with natrojarosite on a thin coating of dufrénite on a garnet sandstone; The globules are zoned from cores of aluminium-rich strengite to rims of iron-rich variscite. At block 14 strengite is associated with libethenite and corkite (AJM 3.1.51-52).

At the Moculta phosphate quarry, Mount Lofty Ranges, South Australia, strengite has been found in small cavities in an iron-rich phosphate rock associated with mitridatite and leucophosphite (AJM 17.1.25).

At the Kiirunavaara Mine, Kiruna, Sweden, strengite occurs in magnetite ore (Dana).

At the John A. Logan mine, Cripple Creek mining district, Colorado, USA, two generations of strengite have been found in thin limonitic fractures in a partly oxidised orthoclase - quartz - pyrite rock associated with cacoxenite and rockbridgeite (MinRec 36.2.179).

At Palermo number 1 mine and the Fletcher mine, North Groton, New Hampshire, USA, strengite occurs as an oxidation product of triphylite (Dana).

At the Midvale mine, Rockbridge county, Virginia, USA, strengite is associated with rockbridgeite (Dana).

Common impurities: Al

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