Hematite

Hardness (Mohs scale): 5.5-6.5; Color: Brownish-red to black, often with a metallic sheen; Luster: Submetallic to dull; Crystal structure: Trigonal (often massive, granular, botryoidal, or oolitic); Cleavage: None; Specific Gravity: 5.2-5.3

Hematite can form in various geological environments. It commonly forms as a primary mineral during magmatic differentiation, as a hydrothermal mineral, and as a sedimentary mineral in banded iron formations (BIFs). It is also a common alteration product of other iron-bearing minerals during weathering. Geologic age varies widely depending on the formation process, with some banded iron formations dating back billions of years (Precambrian).

Hematite is overwhelmingly used as the most important ore of iron (Fe), which is vital for steel production. It is also used as a pigment (e.g., in paints, cosmetics, and polishing rouge), and as an abrasive. Polished hematite is sometimes used in jewelry, though it is not a traditional 'gemstone'.

Hematite is the primary iron ore and has been used by humans for thousands of years, with evidence of its use as a pigment dating back over 164,000 years. Its red streak is a very distinctive characteristic, leading to its name which is derived from the Greek word 'haima' meaning blood.

To identify hematite in the field, key characteristics to look for include its metallic to earthy luster, high density (it feels heavy for its size), and most importantly, its characteristic reddish-brown streak (even if the specimen itself is black or silvery). It will not be magnetic unless it contains significant magnetite impurities. It is commonly found in vast sedimentary deposits (banded iron formations) around the world, as well as in some igneous and metamorphic rocks. Good places to find it include the Lake Superior region in North America, Brazil, and parts of Australia. For collectors, massive or botryoidal forms are common; crystalline specimens are highly prized.