The name given to the siliceous iron formation from which the high-grade iron ores of the Lake Superior district have been derived. It consists chiefly of fine-grained silica mixed with magnetite and hematite. As the richer iron ores approach exhaustion in the United States, taconite becomes more important as a source of iron. To recover the ore mineral in a usable form for the production of iron, taconite must be finely ground, and the magnetite or hematite concentrated by a magnetic or other process. Finally, the concentrate must be agglomerated into chunks of size and strength suitable for the blast furnace.