Alternative iron source produced by heating an iron ore (generally having 65 to 70 percent iron) at a temperature high enough to burn off its carbon and oxygen content (a process called reduction) but below iron's melting point(1535°C or 2795°F). The output is sold as pellets or briquettes (called hot briquetted iron or HBI) and contains from 90 to 97 percent pure iron, the rest being mainly carbon with trace amounts of other impurities. DRI is consumed primarily by mini steel mills (which can melt only rich sources of metal, such as steel scrap, but not iron ore) to improve the quality of their steel. Since the reduction process consumes prodigious amounts of natural gas, it is economically viable only where natural gas is abundant and relatively cheap (such as in Trinidad & Tobago). Also called sponge iron due to its porous nature.