sedimentary

Chert (Jasper variety)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Brown, reddish-brown, and black; Luster: Dull to waxy; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65.

Hardness: 6
Color: Brown, reddish-brown, and black
Luster: Dull to waxy

Identified March 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of silica from groundwater or the accumulation of silica-rich organic remains (like radiolaria) in marine environments. This specimen likely dates from the Phanerozoic eon. Iron impurities give it the characteristic brown/red jasper-like hues.

Uses & applications

Historically used for making stone tools (arrowheads/scrapers) due to its sharp edges. Modernly used for landscaping, aggregate in construction, and lower-grade jewelry (cabochons) or as polished decorative stones.

Geological facts

Chert has been used by humans for over 2 million years. Its ability to produce sparks when struck against steel made it essential for early 'flintlock' firearms and fire-starting kits.

Field identification & locations

Identify in the field by its hardness (it will scratch glass) and its conchoidal fracture, which creates curved, shell-like surfaces on broken edges. Common in limestone formations or as river pebbles.