Formula: FePO4.2H20 Monoclinic
Description: Phosphosiderite forms reddish or purplish elongated to radial fibrous crystals in pegmatites and in as a surface or groundwater precipitate in phosphorous-rich environments. It is often associated with other phosphate minerals such as members of the apatite group, lithiophyllite, strengite and rockbridgeite.
DODGE COUNTY: Phosphosiderite is tentatively identified as a microscopic component of the oolites in the Mayville iron ore, as exposed in old mines and outcrop in sec. 1, 12 and 13 T.11N. R.16E, near Neda. (Hawley and Beavan, 1934).
SAUK COUNTY: An “iron phosphate”, possibly phosphosiderite, was found as an accessory at the Illinois Mine, about 3 miles southwest of Freedom and elsewhere in the Baraboo Iron Range (Leith, 1904).