sedimentary

Banded ironstone pebble

Banded iron formation (BIF), chiefly quartz/chert and iron oxides; possibly hematite–magnetite-rich jasper

AI-generated identification · may be incorrect

Hardness about 6–7 Mohs; fine-grained, opaque, brown to dark gray with distinct iron-rich banding, earthy to submetallic luster, and no obvious cleavage. The rounded shape indicates natural water abrasion or tumbling.

Identified September 13, 2026More sedimentary →

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Physical properties

Formation & geological history

Chemical sediment deposited in Precambrian oceans, commonly 3.8–1.8 billion years ago, when dissolved iron precipitated alongside silica during changes in oceanic oxygen levels. Later lithification and weathering produced the banded pebble.

Uses & applications

Used as iron ore when sufficiently iron-rich; otherwise collected as an attractive lapidary stone and sometimes polished for ornamental pieces.

Geological facts

BIFs preserve evidence of Earth’s early oxygenation and are major sources of global iron. The image’s appearance is also compatible with iron-rich jasper or chert, which cannot be distinguished confidently without testing.

Field identification & locations

Look for alternating silica and iron-oxide bands, high density, and often a red-brown streak; magnetite-rich pieces may attract a magnet. Common in Precambrian shields, including Australia, India, Brazil, Canada, and South Africa.