sedimentary

Chert (Jasper variety)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Brown, dark grey, reddish-brown; Luster: Dull to waxy; Structure: Microcrystalline (Cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Brown, dark grey, reddish-brown
Luster: Dull to waxy

Identified June 16, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Brown, dark grey, reddish-brown; Luster: Dull to waxy; Structure: Microcrystalline (Cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or by chemical precipitation in saltwater environments. Typically found in marine sedimentary layers from various geological ages.

Uses & applications

Historically used for making stone tools due to conchoidal fracture. Modernly used in landscaping, as road aggregate, and for lapidary work (jewelry/polished stones).

Geological facts

Chert is so hard it can scratch steel. It was one of the most important minerals for early humans to create arrowheads and scrapers.

Field identification & locations

Identify by its waxy luster, smoothness when wet, and sharp edges where broken. Commonly found in riverbeds, glacial deposits, and as nodules in limestone.