Formula: Mn2+5(PO4)2(OH)4
Anhydrous phosphate containing hydroxyl, manganese-bearing mineral
Specific gravity: 3.74 calculated
Hardness: 4
Streak: Pale yellow
Colour: Pale yellow, occasionally light reddish orange to light reddish brown
Common impurities: Fe,Cu,Zn,Pb,Al,V,As,H2O

Sedimentary environments
Metamorphic environments


The type locality is the Iron Monarch open cut, Iron Knob, Middleback Range, Eyre Peninsula, South Australia, which is one of only two localities where gatehouseite has been reported to date (January 2021). Here gatehouseite occurs as a secondary mineral forming overgrowths on arsenoclasite in cavities in a matrix of hematite, hausmannite, baryte and carbonates at a sedimentary iron-manganese ore deposit, probably formed by reaction of phosphorus-rich fluids with hausmannite at low temperature (AM 79.185-189, HOM, Webmin). Other associated minerals include shigaite, triploidite, sussexite, shigaite, pyrobelonite and manganoan ferroan calcite (HOM, Mindat). Individual crystals of are rare and less than 100 microns in length; it usually occurs as intergrown crystals (Mindat).

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