metamorphic

Polished tiger iron

Tiger iron, a banded iron formation composed chiefly of jasper/chert, hematite or magnetite, and crocidolite (riebeckite)

AI-generated identification · may be incorrect

Opaque, polished stone with reddish-brown, gold, and dark gray-green bands; quartz-rich portions have Mohs hardness about 6.5–7, while iron oxides are softer. Fine-grained, with no visible cleavage and a silky-to-glassy polish.

Identified September 28, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed as ancient chemical sediments rich in silica and iron, then altered and banded during diagenesis and metamorphism. Many deposits are Precambrian, roughly 2–3 billion years old.

Uses & applications

Used for cabochons, beads, carvings, and collectible polished stones; iron-rich layers may also be mined as iron ore.

Geological facts

Its alternating jasper, iron-oxide, and fibrous amphibole bands create the distinctive tiger-like pattern.

Field identification & locations

Look for curved or parallel red, gold, and dark bands; tiger iron is especially associated with Western Australia and South Africa. The small polished piece shown is likely worth about $5–$25, depending on pattern and workmanship.