Taconite

Taconite () is a variety of banded iron formation, an iron-bearing (over 15% iron) sedimentary rock, in which the iron minerals are interlayered with quartz, chert, or carbonate. The name taconyte was coined in the 19th century by Horace Vaughn Winchell – son of Newton Horace Winchell, the Minnesota state geologist – during their pioneering investigations of the Precambrian Biwabik Iron Formation of northeastern Minnesota within the Mesabi Range. 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 unnamed iron-bearing rock as the 'taconic rock' or taconyte. Following development of high grade direct shipping iron ore deposits on the Mesabi Range, containing up to 65% iron and as little as 1.25% silica, miners termed the unaltered iron-formation wall rock taconite.

The iron content is generally 30% to 35%, and the silica content generally around 45%. The iron is commonly present as magnetite, iron silicates, and iron-bearing carbonates, and locally martite (hematite) formed by oxidation of magnetite. Horizons containing magnetite as the dominant mineral have been extensively mined since 1955 to produce iron ore pellets; the term 'taconite' has consequently been colloquially adapted to describe the magnetite iron-formation ores (taconite iron ore), the mining, milling, magnetic separation, and agglomerating process (taconite process), and the product iron ore pellets (taconite pellets).