sedimentary

Banded iron formation (ironstone), likely hematite–magnetite jasper

Banded iron formation (BIF), chiefly Fe₂O₃ hematite, Fe₃O₄ magnetite, and SiO₂ quartz/chert

AI-generated identification · may be incorrect

Dark gray to black, metallic-to-earthy luster with rusty yellow-orange iron-oxide staining and pale quartz/chert bands; typically hard (Mohs 6–7), dense, fine-grained, and may be weakly magnetic if magnetite-rich. The specimen appears naturally weathered and rounded, possibly lightly polished.

Identified August 20, 2026More sedimentary →

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At a glance

Common name: Banded iron formation (ironstone), likely hematite–magnetite jasper
Scientific name: Banded iron formation (BIF), chiefly Fe₂O₃ hematite, Fe₃O₄ magnetite, and SiO₂ quartz/chert
Category: sedimentary
Identified: August 20, 2026
Method: Standard

AI Estimated Value

About $5–$30 for a common hand specimen; $30–$150 for especially colorful, polished, or strongly banded 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 formed when dissolved iron precipitated with silica in ancient oceans, commonly 2.5–3.8 billion years ago during oxygenation of Earth’s atmosphere. Later compaction, diagenesis, and low-grade metamorphism produced the banding.

Uses & applications

Used as a major iron ore where sufficiently iron-rich; attractive pieces are sold as lapidary rough, cabochons, bookends, and decorative stone. It is not generally a construction aggregate in specimen form.

Geological facts

Alternating iron-rich and silica-rich layers record dramatic changes in ancient seawater chemistry. Rust-colored surfaces commonly reflect weathering of pyrite, hematite, or magnetite.

Field identification & locations

Identify by dense black-gray rock, parallel pale bands, rusty staining, and a streak or magnetism test; quartz bands resist scratching, while magnetite-rich portions attract a magnet. Common in Australia, Canada, Brazil, India, South Africa, and Minnesota, USA.