Hematite

Hardness: 5-6 (Mohs scale), Color: Typically dark brown to black, can appear reddish-brown when thin. Luster: Submetallic to earthy. Crystal structure: Trigonal (rhombohedral) system. Cleavage: Poor basal cleavage. Specific Gravity: 5.26.

Hematite forms in various geological environments but is primarily found in sedimentary deposits, specifically banded iron formations (BIFs), which are ancient (Precambrian) chemical sediments. It can also form during hydrothermal processes, in contact metamorphic deposits, and as a weathering product of other iron-bearing minerals. Its formation is often linked to the presence of water and oxygen reacting with iron. Geological Age: Primarily Precambrian for large sedimentary deposits (BIFs), but can form at any age.

Industry: The primary ore for iron production (steelmaking). Used as a heavy medium in 'heavy media separation' processes (e.g., coal washing). Used as a red pigment (rouge) for polishing glass and jewelry. Jewelry: Polished beads (like those in the image), cabochons, and carvings, often used in 'mourning jewelry' or for its metallic luster. Construction: Not typically used as a construction material itself, but the steel produced from it is vital for construction.

Hematite is the most important iron ore mineral. Its name comes from the Greek word 'haima' meaning 'blood', due to the reddish color of its powdered form. It was used as a pigment in painting since prehistoric times. High-quality hematite can be polished to a mirror-like sheen, making it popular for jewelry and ornamental objects, especially during the Victorian era ('Black Diamond' jewelry).

Field Identification: Distinctive reddish-brown streak (when rubbed on unglazed porcelain – a key identifier), high density (it feels heavy for its size), and submetallic luster. Often found in association with other iron oxides and silicates. Common Locations: Significant deposits are found worldwide, including the Lake Superior region (USA and Canada), Brazil (Minas Gerais), Australia (Pilbara), and Ukraine (Kryvyi Rih). Tips for Collectors: Look for its characteristic streak and density. Faceted hematite beads, as seen, are quite common in jewelry. Natural crystals can be platy (showing a micaceous habit called 'specular hematite') or reniform ('kidney ore').