sedimentary
Banded Iron Formation (Jaspilite / Hematite Jasper)
SiO2 + Fe2O3 (Quartz with Hematite/Magnetite)
Hardness: 6.5-7 on Mohs scale. Color: Red jasper layers mixed with dark silver-grey metallic hematite or magnetite. Luster: Dull to sub-metallic. Crystal Structure: Microcrystalline (trigonal quartz with hexagonal hematite). Specific gravity: 3.0-4.5.
- Hardness
- 6
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Red jasper layers mixed with dark silver-grey metallic hematite or magnetite. Luster: Dull to sub-metallic. Crystal Structure: Microcrystalline (trigonal quartz with hexagonal hematite). Specific gravity: 3.0-4.5.
Formation & geological history
Formed during Precambrian times (2.4 to 1.8 billion years ago) when oxygen released by early photosynthetic cyanobacteria oxidized dissolved iron in ancient oceans, precipitating layered iron oxides and chert onto the sea floor.
Uses & applications
Primary source of iron ore globally for steel production; decorative cabochons, lapidary carvings, and landscape stones; educational and geological collection specimens.
Geological facts
Banded iron formations represent crucial evidence of the 'Great Oxidation Event', which fundamentally changed Earth's atmosphere and permitted the evolution of complex life.
Field identification & locations
Identified by distinct alternating bands of reddish microcrystalline quartz (jasper) and dark, dense, metallic iron minerals (hematite/magnetite), which often attract magnets slightly. Commonly found in ancient Precambrian shield areas such as the Lake Superior region, Western Australia, South Africa, and Brazil.
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