The iron in every steel beam was forged inside exploding ancient stars
Iron is the fourth most common element in Earth's crust, yet almost none of it can be used. Most is locked in silicate minerals too costly to smelt, so industry relies on rarer iron oxides. Those ores feed nearly all steel production, and one analyst ranked them second only to oil in economic importance.
Iron's story begins in space. It forms by nuclear fusion in stars, and most probably came from massive stars that died as supernovae. Earth's core is thought to be largely iron, beyond reach, and pure metallic iron is almost absent at the surface except in meteorites. The ores that matter are rich in iron oxides, coloured anywhere from dark grey and bright yellow to deep purple and rusty red. Magnetite holds 72.4% iron, hematite 69.9%, with goethite, limonite and siderite lower.
Humans have worked their way down the grades. Prehistoric people smelted laterite, and until the industrial era most iron came from goethite or bog ore, including during the American Revolution and the Napoleonic Wars. Industrial nations then mined rich hematite, around 70% iron, so pure it could go straight into a blast furnace. After the Second World War, as American high-grade deposits ran out, attention shifted to lower-grade magnetite and taconite, the North American name for ancient banded iron formations.
Poorer rock needs heavy processing. A magnetite deposit can pay with as little as about 25% iron: crushed and ground to powder finer than 45 micrometres, it passes magnets that pull out the iron, leaving quartz behind, to give concentrate above 70%. Each tonne of concentrate leaves roughly 2.5 to 3 tonnes of tailings, and about 130 million tonnes are dumped each year.
The business runs on volume and railways. Around 98% of mined ore becomes steel, and in 2021 iron ore made up 93% of all metal mined. Annual output averages 2 billion tonnes. Vale of Brazil leads, followed by Rio Tinto and BHP, and in 2004 Australia and Brazil together supplied 72% of seaborne trade.
Source: Iron ore
