Brown-red crystal of lepidocrocite on goethite. From the Great Perran iron lode, Cornwall, England. Field of view is about 5 mm. (Photo courtesy Dakota Matrix Minerals; unauthorized reproduction is prohibited.)

Formula: FeO(OH) Orthorhombic


Lepidocrocite is a polymorph of goethite and is often found associated with it. The two minerals are very similar in physical properties, and it is likely that the mineral is more common in the state than the localities would indicate. For example, the type material for goethite from Eiserfeld, Germany has been subsequently shown to be lepidocrocite (Palache, Berman and Frondel, 1944).

MARATHON COUNTY: Scaly deep red crystals in rosettes up to 1 mm across are found in vugs in altered siderite associated with goethite in the pegmatites of the Wausau pluton such as in exposed in the rotten granite quarries south of Rib Mountain, in Sec. 19 and 20 T.28N R.7E (Falster, 1987; Falster et al., 2000).

ROCK COUNTY: Lepidocrocite forms as an alteration product of pyrite with jarosite, alunite and gypsum in the St. Peter sandstone exposed in the silica sand quarry near Hanover (Odom, Willard and Lassin, 1979).