Banded Iron Formation (Hematite/Magnetite-rich)

Physical Properties

Hardness: 5-6 on Mohs scale; Color: Reddish-brown to dark gray/black; Luster: Dull to metallic; Structure: Fine-grained, often layered; Cleavage: None; Specific Gravity: 4.5-5.3.

Formation & Geological History

Formed in ancient seawater as a result of oxygen release by early photosynthetic organisms, causing dissolved iron to precipitate into layers. Primarily Precambrian in age (3.8 to 1.8 billion years ago).

Uses & Applications

The primary global source of iron ore for steel production; also used as decorative stone and in jewelry (as Tiger Iron or polished Hematite).

Geological Facts

These formations provide the best evidence for the Great Oxidation Event, where Earth's atmosphere first became oxygen-rich due to cyanobacteria.

Field Identification & Locations

Identify by its high density (heavy for its size) and distinct reddish-brown streak on porcelain. Commonly found in major Precambrian shields like those in Western Australia, Brazil, and the Lake Superior region.

Identified on: 5/3/2026

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