Taconite is a variety of banded iron formation, an iron-bearing sedimentary rock, in which the iron minerals are interlayered with quartz, chert, or carbonate. The name "taconyte" was coined by Horace Vaughn Winchell (1865–1923) – son of Newton Horace Winchell, the Minnesota State Geologist – during their pioneering investigations of the Precambrian Biwabik Iron Formation of northeastern Minnesota. He believed the sedimentary rock sequence hosting the iron-formation was correlative with the Taconic orogeny of New England, and referred to the unfamiliar and as-yet-unnamed iron-bearing rock as the 'taconic rock' or taconyte.
Taconite
Processed taconite pellets as used in the steelmaking industry, with a US quarter shown for scale.
Banded iron formations are distinctive units of sedimentary rock consisting of alternating layers of iron oxides and iron-poor chert. They can be up to several hundred meters in thickness and extend laterally for several hundred kilometers. Almost all of these formations are of Precambrian age and are thought to record the oxygenation of the Earth's oceans. Some of the Earth's oldest rock formations, which formed about 3,700 million years ago (Ma), are associated with banded iron formations.
Banded iron formation, Karijini National Park, Western Australia
2.1 billion year old rock from North America showing banded iron formation, displayed in Dresden, Saxony, Germany
Banded iron formation from the Barberton Greenstone Belt, South Africa
Close-up of banded iron formation specimen from Upper Michigan