hematite

Hematite is an iron oxide mineral with the chemical formula Fe2O3. It is one of the most common minerals in Earth’s crust and a principal iron ore. Hematite varies in color from deep reddish-brown to gray, and it leaves a reddish to reddish-brown streak when rubbed on a porcelain plate. The luster ranges from metallic or submetallic to earthy, and crystals are often tabular or plate-like, though the mineral is frequently found in massive forms.

Hematite forms by oxidation of iron-bearing minerals in rocks, by hydrothermal processes, and in sedimentary environments such as iron-rich concretions and banded iron formations. It occurs in many rock types, including metamorphic, igneous, and sedimentary rocks. The two common varieties are specular hematite, which has a metallic luster and reflective plates, and earthy hematite, which is dull and earthy. Hematite is characteristically dense, with a specific gravity around 5.0–5.3, and has a hardness of about 5.5–6.5 on the Mohs scale.

Economically, hematite is a major source of iron ore. It has also been used as a pigment since antiquity (red ochre) and remains popular in jewelry, where polished hematite cabochons are valued for their metallic luster. The name hematite derives from the Greek haima, meaning “blood,” a reference to its color in ore form or powder.