Formula: Ca2Mg(AsO4)2.2H2O
Hydrated normal arsenate, roselite group
Forms a series with roselite
Specific gravity: 3.52
Hardness: 3 to 4
Streak: Pale pink
Colour: Pale pink to red
Common impurities: Co

Hydrothermal environments

Wendwilsonite is a rare secondary mineral in cobalt-bearing hydrothermal mineral deposits. There are two type localities, Sterline Hill mine, New Jersey, USA and Arhbar mine, Bou Azzer, Morocco.

At Coahuila, Mexico, a sample of wendwilsonite crystals on calcite has been found (AM 72.217-221).

At the Arhbar mine, Bou Azzer, Morocco, wendwilsonite is associated with talmessite and erythrite on altered ore and calcite gangue (Dana, HOM, AM 72.217-221). The common paragenesis, where a sequence is visible, consists of erythrite, followed by wendwilsonite or roselite, followed by talmessite, and possibly a second generation of erythrite (AM 72.217-221).

At the Sterling Hill mine, New Jersey, USA, wendwilsonite occurs as 0.5 mm crystals with calcite crystals on serpentine which encrusts manganoan calcite with very sparse franklinite and willemite. Wendwilsonite is very rare at this locality (Dana, AM 72.217-221).

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