sedimentary

Banded Iron Formation

Banded Iron Formation (BIF)

AI-generated identification · may be incorrect

Hardness: 5-7. Color: Alternating bands of dark gray/black (hematite/magnetite) and red/brown (chert/jasper). Luster: Metallic to dull. Structure: Fine-grained, layered. Specific Gravity: 3.0-5.0.

Hardness: 5-7
Luster: Metallic to dull

Identified July 14, 2026More sedimentary →

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Physical properties

Hardness: 5-7. Color: Alternating bands of dark gray/black (hematite/magnetite) and red/brown (chert/jasper). Luster: Metallic to dull. Structure: Fine-grained, layered. Specific Gravity: 3.0-5.0.

Formation & geological history

Formed in ancient oceans during the Precambrian era (3.8 to 1.8 billion years ago) when photosynthetic organisms began producing oxygen, which caused dissolved iron to precipitate out of seawater as iron oxides.

Uses & applications

Primary global source of iron ore for steel production; also used as ornamental stone and for lapidary work including cabochons.

Geological facts

BIFs are among the oldest rocks on Earth and provide evidence for the Great Oxygenation Event, a critical period in Earth's atmospheric history.

Field identification & locations

Identify by distinct rhythmic layering of iron-rich and silica-rich minerals. Often magnetic if magnetite is present. Common in ancient shield areas like Minnesota (Mesabi Range), Western Australia, and Brazil.