sedimentary

Banded iron formation fragment (likely hematite–magnetite-rich ironstone)

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

AI-generated identification · may be incorrect

Dark brown-black, fine-grained, massive to subtly banded, with metallic to earthy luster; hardness about 5–6.5, specific gravity roughly 3.0–5.2, and no prominent cleavage. The exposed dark layers may be weakly magnetic if magnetite-rich.

Identified September 5, 2026More sedimentary →

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At a glance

Common name: Banded iron formation fragment (likely hematite–magnetite-rich ironstone)
Scientific name: Banded iron formation; chiefly hematite (Fe₂O₃), magnetite (Fe₃O₄), and silica/chert (SiO₂)
Category: sedimentary
Identified: September 5, 2026
Method: Standard

AI Estimated Value

About $2–$15 for a small common fragment; $20–$75 if strongly banded, polished, or magnetite-rich.

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, commonly 2.5–1.8 billion years ago, as dissolved iron oxidized and precipitated in alternating iron- and silica-rich layers. The rounded form indicates later stream or beach transport and abrasion.

Uses & applications

Major industrial source of iron ore after concentration and beneficiation; attractive polished pieces are used as lapidary specimens and educational material.

Geological facts

Banded iron formations record the Great Oxidation Event and the rise of oxygen-producing organisms. Weathering commonly produces red, brown, and black iron-oxide surfaces.

Field identification & locations

Look for dense weight, rusty streaks, fine alternating dark and pale layers, and possible magnetism; a streak test and magnet help distinguish it from ordinary basalt. Common in the Lake Superior region, Australia, Brazil, India, and South Africa.