Sedimentary

Banded Iron Formation (BIF) or Jasperite

Banded Iron Formation (Fe2O3 + SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (due to silica). Color: Alternating bands of reddish-brown, yellow, orange (iron oxides like hematite, limonite) and dark green, grey, or black (magnetite, shale, or chert). Luster: Dull to waxy, often polished smooth by water. Structure: Microcrystalline quartz interbedded with iron oxides.…

Hardness: 6
Luster: Dull to waxy, often polished smooth by water

Identified August 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in shallow seas over 2 billion years ago during the Precambrian era when early photosynthetic organisms began producing oxygen, which reacted with dissolved iron in the oceans to precipitate alternating layers of iron oxides and silica. Often found as water-worn pebbles in glacial drift or riverbeds.

Uses & applications

Major ore of iron for the steel industry. Attractive, polished specimens are used in lapidary arts, jewelry, and collected by rockhounds.

Geological facts

Banded Iron Formations are among the oldest rocks on Earth and represent a crucial period in planetary history (the Great Oxidation Event). Some forms with high jasper content are called Jaspilite.

Field identification & locations

Identified by distinct, parallel bands of alternating colors, usually containing iron and silica. Common in areas like the Great Lakes region (e.g., Lake Superior). Tips: Wetting the stone (as shown) highlights the bands and colors. Often slightly magnetic if magnetite is present.