Banded Iron Formation (BIF) / Jasper

Physical Properties

Hardness: 6.5-7 (Mohs), Color: Dark red to brownish-black bands, Luster: Dull to sub-metallic, Crystal Structure: Trigonal/Microcrystalline, Cleavage: None, Specific Gravity: 3.0-4.5 (depending on iron content)

Formation & Geological History

Formed in ancient seawater billions of years ago (typically Precambrian) through the precipitation of recurring layers of iron oxides and silica. They represent a record of the oxygenation of Earth’s atmosphere.

Uses & Applications

Major industrial source of iron ore; semi-precious stone used in jewelry (as Jasper or Tiger Iron) and lapidary work.

Geological Facts

BIFs are the primary source of the world's iron ore supplies. They were largely formed during the 'Great Oxidation Event' when photosynthetic bacteria first began releasing oxygen into the ocean.

Field Identification & Locations

Identify by the alternating red (chert/jasper) and black (hematite/magnetite) bands. They are heavy for their size due to iron content and often show a slight magnetic pull. Common in Lake Superior region, Australia, and Brazil.

Identified on: 5/20/2026

Mode: Standard