sedimentary

Banded iron formation pebble

Banded iron formation (BIF), chiefly hematite/magnetite with chert or jasper

AI-generated identification · may be incorrect

Hardness about 5.5–6.5; metallic to earthy luster; rusty red-brown, ochre, gray, and black banding. Dense, fine-grained, with no visible cleavage; black bands may be magnetic if magnetite-rich.

Identified August 10, 2026More sedimentary →

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Physical properties

Hardness about 5.5–6.5; metallic to earthy luster; rusty red-brown, ochre, gray, and black banding. Dense, fine-grained, with no visible cleavage; black bands may be magnetic if magnetite-rich.

Formation & geological history

Chemical sediment formed when dissolved iron precipitated with silica in ancient oceans, commonly during the Precambrian roughly 3.8–1.8 billion years ago; later lithified and rounded by stream or beach transport.

Uses & applications

Used as iron ore where sufficiently iron-rich; polished pieces are popular lapidary and collector specimens, but this small rounded pebble has mainly decorative value.

Geological facts

Alternating iron-oxide and silica layers record changing ocean chemistry and oxygenation. The strong, unusually regular striping is characteristic of BIF, though the specimen may also be a jasper-rich ironstone.

Field identification & locations

Look for dense parallel red/yellow/gray bands, streaking, and possible attraction to a magnet; a streak test can distinguish hematite (reddish-brown) from magnetite (black). Common in Australia, Brazil, India, South Africa, Ukraine, and North America.