Iron mineral, Fe₂O₃; one of the main ores for iron; sp. gr. 4.9–5.3; hardness 5–6; trigonal; steel-grey to black, often iridescent, compact varieties dull to bright red; red to reddish-brown streak; metallic lustre; crystals tabular or rhombohedral with curved, striated faces, also occurs as columnar, mammillated, and botryoidal masses; no cleavage; widely distributed as an accessory mineral in igneous rocks, hydrothermal veins, as a rock-forming mineral in sedimentary rocks, as a primary mineral, as concretions or a cementing agent, and as a replacement for other minerals. Bedded ores of hematite form huge deposits in the Precambrian of N. America and elsewhere. Specularite is a grey or black variety of hematite with a brilliant metallic lustre that occurs in foliated masses or aggregates of tabular crystals. See banded iron formation (bif).