Hematite, a Shape-shifting Mineral From the Stone Age

Hematite is an iron oxide in its base form that is 70 percent iron and 30 percent oxygen, and has the chemical formula of Fe₂O₃. As one of the most abundant minerals on the planet, it is perfect for mining to produce iron and iron-based derivatives like steel.

Even though it is plentiful, hematite isn't usually found on Earth on its own; rather it is generally found mixed together with other minerals like magnetite.

Hematite stone "forms as a reaction of hot magmas with surrounding materials and likely eroded into concentrated layers of downdip sedimentary beds, separating out via gravity distribution. Hematite can also precipitate out of lake waters forming a bed on lake bottoms," says Brad LeBlanc, senior geoscientist for Sweet Lake Land & Oil, an oil refinery in Louisiana, in an email interview.

As hematite can be formed in different ways, it can have different physical traits. For anyone learning geology, this makes the rock rather hard to identify based on just appearance alone.

Intuitively it's not easy to think that a rainbow metallic crystal is actually the same kind of mineral as a black rough specimen, but these are both forms of hematite.

The mineral does have one big "tell," though, and it harkens back to its nickname of "bloodstone." Regardless of how hematite looks, due to its high iron and oxygen content, when it's scratched against anything it always leaves a red powder.

"If you're unsure about the specimen in your hands you can scratch it against something – and if it streaks reddish to reddish brown it's likely hematite," says LeBlanc.

Back when Earth was covered in primordial oceans about 2.4 billion years ago, there was naturally an abundance of iron in the water. When early aquatic plant life that could process sunlight and undergo photosynthesis started forming, the oceans began filling with oxygen.

This oxygen bound with the iron in the water, forming rust particles. Over time, these sank to the bottom of the ocean's floor, compressing into banded iron ore deposits which are the primary source of hematite today. This accumulation continued for hundreds of millions of years.

Along with hematite in these sedimentary iron deposits, there's also magnetite, another primary source of iron, with a slightly different chemical formula of Fe₃O₄. The mixing of these two minerals in different quantities is one of the ways hematite can take on different forms.

While hematite is mainly mined for iron, there are several other uses for the mineral going back to the earliest civilizations.

Hematite is one of the main ingredients of "red ochre," a pigment used for paints, makeup, glazes and early cave drawings in paleolithic eras. Rust and rust-derived minerals naturally hue red, so early civilizations always had access to this color. Red ochre was also used in paintings of the Renaissance era.

Since hematite can present itself in highly metallic and crystalline forms, it's also used in jewelry. When polished or tumbled, the mineral can give off a smooth metallic appearance, making it perfect for beads of all shapes and sizes.

The mineral has also been used as a "healing stone" that is said to bring relief from medical problems like anemia, leg cramps and insomnia. These claims, though, have no scientific basis.

But there is a real medical use for hematite: It can stop X-rays and so it is used in radiation shielding for medical equipment.

However, these other uses for hematite don't make up a significant portion of the mineral's use overall, not when compared with iron production.

While hematite can be found virtually everywhere in the world, large quantities of it are mined in places like China, Brazil, Venezuela, Australia and South Africa, as well as across the U.S. and Canada. Some of these mines remove more than 100 million tons of iron ore (which includes hematite, magnetite and other products) every year.

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.