Banded Iron Formation (BIF) / Tiger Iron

Physical Properties

Hardness: 5.5-7 (Mohs), Color: Alternating bands of silver-grey (hematite), black (magnetite), and often red (jasper), Luster: Metallic to sub-metallic, Structure: Banded/laminated

Formation & Geological History

Formed in marine environments during the Precambrian era (approx. 2.4 to 1.8 billion years ago) through the precipitation of iron oxides and silica as oxygen levels rose in Earth's atmosphere

Uses & Applications

Primary global source of iron ore for steel production; decorative use in lapidary, jewelry, and as ornamental stone

Geological Facts

These formations reflect the 'Great Oxygenation Event' when early life began producing oxygen through photosynthesis, causing dissolved iron in the oceans to rust and settle on the seafloor

Field Identification & Locations

Identify by distinct rhythmic layering of heavy metallic bands and silica; highly magnetic if magnetite-rich; found in ancient cratons like the Pilbara (Australia) or Lake Superior (USA)

Identified on: 4/28/2026

Mode: Standard