References in periodicals archive ?
Groutite, an orthorhombic trimorph of (monoclinic) manganite and feitknechtite, is a rare species known in good specimens chiefly from the Iron Range of Minnesota (in 1980 some superb specimens were collected in the Roberts mine, Cayuna Range, Crow Wing County).
The yellow patina (already mentioned) is lepidocrocite, chemically identical with goethite, its trimorph.
These are sparkling, intense bluish green crusts of microcrystals lining seams in tough quartz/limonite matrix, some also harboring microcrystals of the extremely rare trimorph ludjibaite.