Iron ore is abundant, but its isolation is an energy-intensive process. The chief ores are the oxides hematite, Fe2O3 and magnetite, Fe3O4, and its carbonate siderite, FeCO3. Iron pyrite, FeS2 contains the iron, but it is difficult to isolate from the sulfur. This ore is used as a source for sulfur. Common useful forms of iron alloys are cast iron, wrought iron, and steel.
Wrought iron is made from cast iron by melting it on a bed of iron oxide.
The purification occurs because the iron oxide bed oxidizes the carbon to carbon monoxide and the sulfur, phosphorus and silicon to their oxides. These oxides become part of the slag. As the iron becomes purer, its melting point rises and it becomes pasty, signaling the time to remove it from the furnace. The slag is then forced out by hammering. Wrought iron created by this process is strong and tough and can be welded and forged.