How Does Hematite Form?

Composition

• A hematite molecule is composed of two iron and three oxygen molecules. Hematite̵7;s chemical formula is Fe2O3, so it is called iron oxide and is an important iron ore, typically composed of 70 percent iron. Hematite is mined to extract the iron, which in turn is used to produce steel, an essential worldwide building material. Hematite can be dark gray with a metallic luster or reddish-brown, or a combination of dark grey and brown with red streaks.

Sedimentary Rock

• Most hematite is found in sedimentary rock formations. Sandstone is common sedimentary rock formed as layers of sediment built up on top of one another from prehistoric oceans more than 1.6 billion to 1.8 billion years ago. Sandstone is typically reddish-brown in color, caused by an abundance of hematite crystal content. These sedimentary hematite crystals formed as evaporating oceans left deposits of iron in the sediment layers. The iron then combined with oxygen molecules created by the process of photosynthesis.

Metamorphic Rock

• Hematite crystals can be found in metamorphic rock formations such as marble. Metamorphic rock is typically formed from limestone under great pressure, for instance, when the earth̵7;s plates shift. Therefore, metamorphic rock is found in mountain ranges and other areas where the earth has experienced cataclysmic shifts. The hematite crystals within the metamorphic rock were formed earlier and trapped in the sedimentary limestone.

Igneous Rock

• Hematite crystals also can be found in igneous rock formations. Igneous rock, such as granite, forms from cooling volcano magma under great pressure far within the earth̵7;s interior. As igneous rock solidifies, it typically takes on a crystallized form. Hematite crystals become trapped in the cooling magma along with other minerals. These hematite crystals are found inside the metamorphic granite that is expelled from volcanoes during eruptions. Igneous hematite is also found in the vicinity of hot springs.