metamorphic

Banded iron formation (ironstone), likely specular hematite–magnetite variety

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

AI-generated identification · may be incorrect

Dark gray to black, metallic to submetallic luster with thin rusty-gold iron-oxide bands and strong foliation/banding. Hardness about 5.5–6.5; quartz-rich portions are harder, with no obvious cleavage; dense, commonly magnetic if magnetite-rich.

Identified September 12, 2026More metamorphic →

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At a glance

Common name: Banded iron formation (ironstone), likely specular hematite–magnetite variety
Scientific name: Banded iron formation (BIF), chiefly hematite (Fe₂O₃), magnetite (Fe₃O₄), and quartz (SiO₂)
Category: metamorphic
Identified: September 12, 2026
Method: Standard

AI Estimated Value

About $10–$40 for a common hand specimen; $50–$200+ for large, highly polished, strongly banded or magnetic specimens.

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 Precambrian marine basins, then compacted, lithified, and variably metamorphosed; most BIF formed roughly 3.8–1.8 billion years ago during ocean oxygenation. The striped appearance reflects alternating silica-rich and iron-rich layers.

Uses & applications

Historically a major iron ore and still mined for steel production; attractive polished pieces are used as lapidary stone, bookends, and mineral specimens.

Geological facts

Rusty colors result from oxidation of iron minerals. Some specimens display strong magnetism and a red-brown streak from hematite.

Field identification & locations

Common in ancient shield regions, especially the Lake Superior district, Western Australia, Brazil, India, and South Africa. Identify by dense fine banding, metallic iron minerals, possible magnetism, and a red-brown streak; a streak and magnet test help distinguish it from ordinary schist.