Hematite is a widely distributed iron oxide mineral, making it one of the most abundant minerals found on the Earth’s surface and in the shallow crust. Its name, derived from the Greek word for blood, alludes to the characteristic reddish hue it displays when powdered. This mineral has long served humanity as the primary ore for iron, forming the foundation of the steel industry. Beyond its industrial importance, finely ground hematite, known as red ochre, has been utilized as a pigment in art and dyes since prehistoric times.
Identifying Hematite
The appearance of hematite is remarkably varied, which can sometimes make field identification challenging. Its external color can range from a mirror-like steel-gray or silver in its metallic form, often called specular hematite, to a dull, earthy reddish-brown in its massive form. The luster also changes dramatically, presenting as splendent metallic in crystalline specimens, or as a dull, non-metallic sheen in specimens with a finer grain structure. Regardless of the specimen’s outward appearance, the most reliable and diagnostic property for identification is its streak.
When a piece of hematite is scraped across an unglazed porcelain plate, it consistently leaves a reddish-brown streak. This streak serves to distinguish it from other metallic minerals like magnetite, which leaves a black streak. Furthermore, hematite is notably dense, meaning a specimen will feel unusually heavy for its size compared to common rock types. Its hardness ranges between 5.5 and 6.5 on the Mohs scale, suggesting it is hard enough to scratch glass but is slightly softer than quartz.
Geological Environments Where Hematite Forms
Hematite forms in a variety of geological settings, with the most significant deposits originating from sedimentary processes. The largest occurrences are found within Banded Iron Formations (BIFs). These ancient rock units, which date back over two billion years, formed as iron and silica precipitated cyclically out of ancient, iron-rich oceans. The resulting layered deposits of iron oxide and chert represent a major global transition when free oxygen first became abundant in the Earth’s atmosphere.
The mineral forms in hydrothermal environments, which involve hot, iron-rich fluids moving through fissures and rock masses. In this setting, hematite precipitates directly from the cooling solution, often filling veins or replacing existing rock minerals. Additionally, hematite is a common product of weathering, where iron-bearing minerals near the surface oxidize. This process of oxidation is what gives many soils and sedimentary rocks their characteristic red or rusty coloration.
Major Global Deposits and Collecting Sites
The world’s largest hematite deposits are concentrated in a few regions, primarily sourced from Banded Iron Formations. Western Australia’s Hamersley Province, particularly the Pilbara region, contains some of the highest-grade hematite deposits globally, fueling a significant portion of the world’s iron ore supply. Brazil’s Quadrilátero Ferrífero, or “Iron Quadrangle,” in Minas Gerais, is another major source, known for its reserves of high-quality hematite. In North America, the Lake Superior region, which includes the Mesabi Range in Minnesota, is known for its iron ore production, much of which originated as hematite-rich BIFs.
Collecting Sites
For the hobbyist collector, hematite can be found in a variety of more accessible locations. Road cuts, stream beds, and areas with highly oxidized red or orange-stained rocks are all potential spots to look for the mineral.
Specific rockhounding locations, such as Graves Mountain in Georgia, are famous for producing iridescent hematite, also known as rainbow hematite. Collecting sites often include the tailings piles or waste rock left over from historical mining operations, where concentrated iron minerals are more easily accessible. Searching areas known for iron-rich sedimentary or volcanic rocks increases the likelihood of finding specimens exhibiting the mineral’s varied forms, from botryoidal kidney ore to micaceous specularite.