sedimentary

Polished banded iron formation (BIF)

Banded iron formation; chiefly hematite/magnetite and microcrystalline quartz (chert), with iron silicates

AI-generated identification · may be incorrect

Typically hard (Mohs 6–7), dense, and finely layered, with metallic gray-black iron bands alternating with red, brown, or golden jasper/chert. The glossy surface is polished; layers reflect sedimentary banding rather than large crystals.

Identified August 11, 2026More sedimentary →

Explore Polished banded iron formation (BIF) 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: Polished banded iron formation (BIF)
Scientific name: Banded iron formation; chiefly hematite/magnetite and microcrystalline quartz (chert), with iron silicates
Category: sedimentary
Identified: August 11, 2026
Method: Standard

AI Estimated Value

About $20–$100 for a hand-sized polished specimen; unusually large, vivid, or expertly finished pieces may sell for $150–$500.

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 marine basins, mainly during the Precambrian (about 3.8–1.8 billion years ago), when dissolved oceanic iron oxidized and precipitated with silica. Later compaction, metamorphism, and weathering produced the dense banded rock.

Uses & applications

Cut and polished BIF is used for decorative stones, bookends, cabochons, and display specimens; iron-rich varieties were historically major sources of iron ore. It has little conventional gemstone value unless exceptionally patterned and well polished.

Geological facts

The alternating bands record changing ocean chemistry and oxygen availability, making BIF important evidence for Earth’s early oxygenation. Some pieces sold as “tiger iron” combine BIF with fibrous asbestos-bearing crocidolite and jasper.

Field identification & locations

Identify it by continuous, wavy iron-oxide and silica bands, high density, and resistance to scratching; a streak test may show red-brown hematite or black magnetite. Major sources include Australia, Brazil, South Africa, India, Ukraine, and North America.