The marcasite was originally in masses up to 12 cm. in diameter. Pseudomorphs of goethite after pyrite crystals in individuals over 2 cm. The largest crystals were 14.5 cm x 7.5 cm. Many tons of goethite pseudomorphs after pyrite was mined from a mineralized fault zone in Cambrian sediments at the Ironton iron mine in the SW Sec. 10 T.12N R.3E, about 2 km.
Goethite occurs as bog iron ore at several points along the Wisconsin River.
4 T.22N R.6E and at Grand Rapids where a 50 cm. thick bed of porous goethite was found.