sedimentary

Banded iron formation (ironstone), possibly hematite–magnetite-rich

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

AI-generated identification · may be incorrect

Typically fine-grained, with alternating dark iron-oxide layers and pale gray-white silica layers; metallic to earthy luster, Mohs hardness about 5–6.5, no prominent cleavage, and commonly dense or weakly magnetic where magnetite is abundant.

Identified September 17, 2026More sedimentary →

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At a glance

Common name: Banded iron formation (ironstone), possibly hematite–magnetite-rich
Scientific name: Banded iron formation; chiefly hematite (Fe₂O₃), magnetite (Fe₃O₄), and chert/microcrystalline quartz (SiO₂)
Category: sedimentary
Identified: September 17, 2026
Method: Standard

AI Estimated Value

About $5–$30 for a common hand specimen; $30–$150+ if unusually banded, polished, or museum-quality.

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 oceans, usually about 3.8–1.8 billion years ago, when dissolved iron oxidized and precipitated alongside silica; later compacted and lithified. The specimen appears weathered and possibly locally brecciated or folded.

Uses & applications

Used as iron ore when sufficiently rich, and collected or cut for decorative stone. Attractive polished pieces may have modest lapidary value.

Geological facts

Banded iron formations record major changes in Earth’s atmosphere and ocean chemistry, especially the rise of oxygen. Dark bands are commonly magnetite or hematite, while light bands are chert.

Field identification & locations

Identify by distinct iron-rich dark bands, pale silica bands, high density, and a streak that may be red-brown (hematite) or black (magnetite); a magnet helps distinguish magnetite. Common in Australia, Brazil, India, South Africa, Canada, and the Lake Superior region.