Ore deposit type: Hydrogenic, BIF
Provenance: Rana Gruber mines, Vesteråli, Norway
Description: Banded iron formation composed of thin alternate bands of hematite ± magnetite (black, massive, fine-grained) and quartz. The banded structure is the result of chemical precipitation from seawater alternately saturated in Fe oxides and silica. Hematite/magnetite and quartz are the products of metamorphism of the original sediment, which probably contained cryptocrystalline oxides and amorphous silica.