Magnetite production was confined to mountain regions in the east and west, and only in Ohio were carbonates mined.
Grains of magnetite occur in serpentine, as an alteration-product of the olivine.
In emery, magnetite in a granular form is largely associated with the corundum; and in certain kinds of mica magnetite occurs as thin dendritic enclosures.
Magnetite, or magnetic iron, the richest of all iron ores, is found in abundance near Wallerawang in New South Wales.
Among the commonest associates of the diamond are quartz, topaz, tourmaline, rutile, zircon, magnetite, garnet, spinel and other minerals which are common accessory constituents of granite, gneiss and the crystalline schists.