English: A mineral is a naturally-occurring, solid, inorganic, crystalline substance having a fairly definite chemical composition and having fairly definite physical properties. At its simplest, a mineral is a naturally-occurring solid chemical. Currently, there are over 5800 named and described minerals - about 200 of them are common and about 20 of them are very common. Mineral classification is based on anion chemistry. Major categories of minerals are: elements, sulfides, oxides, halides, carbonates, sulfates, phosphates, and silicates.

The oxide minerals all contain one or more oxide anions (O-2).

Hematite is a common iron oxide mineral (Fe2O3). It varies in appearance, from nonmetallic-lustered and brick red-colored to metallic-lustered and silvery-gray colored. Brick red hematite is often powdery / earthy or finely granular or oolitic. Silvery-gray hematite (micaceous hematite) is less common and results from mild to moderate levels of metamorphism. Hematite ranges in hardness from soft to moderately hard (about 1 to 6 on the Mohs Hardness Scale). Regardless of a specimen’s color or luster, hematite will always leave a brick red-colored streak, which is its most diagnostic physical property.

This specimen is earthy hematite, sometimes referred to as "red ochre".

Locality: undisclosed / unrecorded site (attributed to the town of Custer) in the Black Hills, western South Dakota, USA

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Photo gallery of hematite:

www.mindat.org/gallery.php?min=1856