The ore occurs in two forms, haematites and limonites; the specular hematites often being grouped, for practical purposes, into two classes - those occurring in porphyry and those occurring in sandstone.
The haematites are found not only in the archean porphyries but in Cambrian limestone and sandstone, and in the sub-Carboniferous formations; while the limonites are confined almost exclusively to the Cambrian.
The bedded haematites and limonites have been little exploited.
The deposits of most commercial importance are the limonites and brown hematites found west of the Cumberland Plateau, and the fossiliferous red hematite which crops out along the eastern base of that plateau.
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