Iron is a foundational element of modern civilization, used predominantly in the production of steel. Its prevalence, however, extends far beyond industrial uses, touching everything from our planet's internal structure to biological processes.
Earth's Planetary Composition
Before focusing on accessible sources, it's important to understand iron's cosmic abundance. Iron is thought to be the most abundant element, by mass, in the entire Earth, forming a large part of its solid inner core and molten outer core. However, this deep-seated concentration is inaccessible for human exploitation. Fortunately, the Earth's crust, a thin layer compared to the core, still contains significant amounts.
Iron in the Earth's Crust
As the fourth most common element in the crust, iron is not typically found in its pure metallic form due to its high reactivity with oxygen. Instead, it exists in compounds with other elements, predominantly in mineral ores. The reddish-brown color of many rocks and soils is a direct result of iron oxidation, commonly known as rust.
Principal Iron Ores and Deposits
The vast majority of iron used in industry is extracted from iron ores, which are rocks containing a high enough concentration of iron minerals to be economically viable. The most important of these minerals are oxides of iron.
Types of Iron Ores
- Hematite ($Fe_2O_3$): This is the most commonly mined iron ore globally. It has a high iron content when pure (up to 70%) and is known as a "direct shipping ore" because it requires less processing before smelting. Despite being chemically purer, hematite deposits often contain more impurities than magnetite ores. Its color ranges from reddish-brown to silvery-grey, but it always leaves a reddish streak.
- Magnetite ($Fe_3O_4$): A black iron oxide with magnetic properties. While the mineral itself has a slightly higher iron content than hematite (up to 72.36% when pure), magnetite ore typically occurs in lower concentrations and requires more processing. Its magnetic properties, however, make it easier to separate from waste rock using magnetic separation.
- Taconite: This is a low-grade iron ore, particularly common in North America's Lake Superior region. It is a form of banded iron formation rich in magnetite. Historically considered waste rock, its economic importance grew as higher-grade ores depleted.
- Goethite and Limonite: These hydrated iron oxides were historically significant but are less important today. Limonite is often a mixture of iron minerals and is known for its yellow to dark brown color.
Banded Iron Formations (BIFs)
Many of the world's most significant iron ore resources come from ancient sedimentary rocks called Banded Iron Formations. These were formed millions of years ago in Precambrian oceans, before the atmosphere contained free oxygen. Photosynthetic bacteria began releasing oxygen, which reacted with dissolved iron in the seawater, causing it to precipitate and form alternating layers of iron minerals and silica on the seafloor. These ancient, layered deposits are now mined extensively across the globe.
Major Global Mining Locations
Iron ore deposits are found worldwide, but commercial mining is concentrated in specific regions. Australia and Brazil are the leading iron ore exporters, with significant production also coming from China, India, and Russia.
Key Mining Regions
- Australia: The Pilbara region of Western Australia holds immense reserves and is the world's largest producer. Ores from this area include high-grade hematite and pisolitic deposits.
- Brazil: A major producer with vast reserves, most notably in the Carajás mine in Pará and the state of Minas Gerais. Brazil exports large quantities of both magnetite and hematite ore.
- China: While a major producer, China's reserves are generally lower grade, averaging about 31% iron. The country relies heavily on iron ore imports to fuel its massive steel industry.
- North America: The Lake Superior region, spanning Minnesota and Michigan in the U.S. and the Labrador Trough in Canada, is a historic and significant source of iron ore, primarily taconite.
| Feature | Hematite Ore | Magnetite Ore | Taconite Ore |
|---|---|---|---|
| Primary Mineral | Hematite ($Fe_2O_3$) | Magnetite ($Fe_3O_4$) | Magnetite-rich BIF |
| Typical Ore Grade | High grade, >60% Fe | Low grade, ~25-45% Fe in rock | Low grade, ~25-45% Fe in rock |
| Processing Required | Less beneficiation; often direct-shipping | Requires extensive concentration via magnetic separation | Requires crushing and magnetic separation into pellets |
| Cost of Extraction | Cheaper due to higher grade and simpler processing | Higher due to extensive processing needs | Higher than high-grade hematite but still economically viable |
| Purity of Final Product | Can contain more impurities | High purity, with fewer impurities | High purity pellets, with controlled specifications |
Other Sources of Iron
Beyond terrestrial mining, iron is also found in several other forms.
Extraterrestrial Sources
Iron-nickel meteorites are remnants of asteroids that melted early in the solar system's history. The denser iron-nickel metal sank to the center, and these pieces are now found when meteorites impact Earth. Before smelting was developed, this 'meteoric iron' was an important source for tools and weapons.
Biological and Atmospheric Sources
- Human Body: Iron is an essential element for almost all living organisms. In the human body, it is a key component of hemoglobin, which carries oxygen in red blood cells. The average human adult carries about 4-5 grams of iron.
- Atmosphere: When meteors enter the Earth's atmosphere, the friction ablates the iron on the surface, which forms free iron atoms. These can react to form compounds in the upper atmosphere, contributing to atmospheric phenomena.
Conclusion
While iron is most concentrated in the Earth's inaccessible core, its most commonly found and industrially useful sources are the mineral ores of the crust, particularly hematite and magnetite found in banded iron formations. Australia and Brazil are leading suppliers of this critical resource. Furthermore, iron's presence is not limited to geology; it is a vital component of meteorites and essential for life on Earth. To learn more about Australia's iron ore resources, visit the Geoscience Australia website.
