These ores are very widely distributed and very abundant in nature, but many deposits cannot be worked profitably. According to chemical composition, ores available for smelting may be classified as follows:

I. Magnetic Iron Ores, or Magnetite (Fe3O4). II. Ferric Oxides or Hematites (Fe2O3).

III. Ferrous Carbonate or Spathic Ores (FeCO3).

IV. Iron Pyrites (FeS2, iron sulphide or fools' gold) is a very abundant ore, but cannot be cheaply smelted because of the difficulty of eliminating the sulphur. However when the sulphur from this ore is extracted in the manufacture of sulphuric acid, the remaining product is profitably smelted, though the iron obtained by this means is but a very small per cent of that smelted. The magnetic ores, the. most valuable of all iron ores, are black, very dense, not so widely distributed as the other ores, have magnetic properties and contain about 72% of iron when pure. The largest known deposits are in the Lake Superior region of the United States.

The hematites are usually red or brown in color, according to the gangue, are widely distributed, and usually free from excessive sulphur and phosphorus. They are employed more in smelting than are other ores because of their abundance.