metamorphic

Banded iron formation (iron-rich metamorphic rock)

Banded iron formation, typically hematite–magnetite–quartz (Fe₂O₃/Fe₃O₄/SiO₂)

AI-generated identification · may be incorrect

Dark gray to black, fine- to medium-grained, with rusty orange weathering from iron oxides and lighter quartz-rich bands. Hardness is about 5.5–7; metallic to earthy luster, no consistent cleavage, and commonly strongly magnetic if magnetite-rich.

Identified September 12, 2026More metamorphic →

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At a glance

Common name: Banded iron formation (iron-rich metamorphic rock)
Scientific name: Banded iron formation, typically hematite–magnetite–quartz (Fe₂O₃/Fe₃O₄/SiO₂)
Category: metamorphic
Identified: September 12, 2026
Method: Standard

AI Estimated Value

About $10–$50 for a common hand specimen; $50–$200+ for large, strongly banded, polished, or exceptionally aesthetic pieces.

Not an official valuation

AI estimate for general interest only — not an appraisal. Actual value depends on condition, provenance, and market demand. Verify with a professional before buying, selling, or insuring.

This identification was generated by AI and may contain errors. Verify important details before relying on them — and never use an AI result to judge whether a specimen is safe to handle. Read the full disclaimer

Physical properties

Formation & geological history

Chemical sediment deposited in ancient Precambrian oceans, then compacted and metamorphosed; most examples formed roughly 3.8–1.8 billion years ago during periods of widespread oceanic oxidation.

Uses & applications

Major iron ore when hematite or magnetite is abundant; attractive pieces are used as lapidary specimens, bookends, and geological teaching samples.

Geological facts

Alternating silica and iron-oxide layers record the rise of oxygen in Earth’s atmosphere and helped create many of the planet’s largest iron deposits.

Field identification & locations

Identify by thin, contrasting iron-rich and quartz-rich bands, heavy weight, rusty staining, and a magnetite response to a strong magnet. Common in the Lake Superior region, Western Australia, Brazil, South Africa, India, and Ukraine.