sedimentary

Banded iron formation fragment (likely hematite–magnetite ironstone)

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

AI-generated identification · may be incorrect

Dark gray-black, metallic to submetallic surface with a rusty brown, granular quartz-rich interior; typically dense and heavy, Mohs hardness about 5.5–6.5, with no obvious cleavage. The specimen appears naturally rounded or tumbled/polished.

Identified August 9, 2026More sedimentary →

Explore Banded iron formation fragment (likely hematite–magnetite ironstone) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

At a glance

Common name: Banded iron formation fragment (likely hematite–magnetite ironstone)
Scientific name: Banded iron formation; chiefly hematite (Fe₂O₃), magnetite (Fe₃O₄), and microcrystalline quartz (SiO₂)
Category: sedimentary
Identified: August 9, 2026
Method: Standard

AI Estimated Value

About $3–$15 for a small common specimen; $15–$50 if attractively polished, strongly banded, or magnetic.

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 sedimentary rock formed when dissolved iron precipitated with silica in ancient oceans, commonly 2.5–1.8 billion years ago during oxygenation of Earth’s atmosphere. Later metamorphism compacted and recrystallized the layers.

Uses & applications

Major global source of iron ore for steel production; attractive polished pieces are sold as display specimens and lapidary material, though this small example has little commercial value.

Geological facts

Alternating iron-oxide and silica bands are diagnostic, although the visible piece may show only a single weathered band. Magnetite-rich material may attract a magnet; hematite-rich material usually does not.

Field identification & locations

Common in the Lake Superior region, Western Australia, Brazil, South Africa, India, and Ukraine. Look for unusual weight, iron staining, dark metallic surfaces, and red-brown streak or powder; a streak test and magnet test help distinguish it from ordinary basalt.