sedimentary

Chert (Jasper / Flint)

Microcrystalline Quartz (SiO2) with Iron Oxides

Hardness: 7 on Mohs scale. Color: Brownish-orange to reddish-brown due to iron impurities. Luster: Dull, earthy to waxy/sub-vitreous. Fracture: Distinct conchoidal fracture with sharp edges. Cleavage: None. Specific gravity: ~2.65.

Hardness: 7 on Mohs scale
Color: Brownish-orange to reddish-brown due to iron impurities
Luster: Dull, earthy to waxy/sub-vitreous

Identified July 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in sedimentary environments through the precipitation of silica-rich solutions or accumulation of siliceous biogenic remnants (such as radiolarian shells). The reddish-orange staining is caused by hematite or goethite iron oxide impurities.

Uses & applications

Historically used by indigenous peoples for stone tools like arrowheads, scrapers, and blades due to its sharp conchoidal fracture. Modern uses include road aggregate, landscape stone, and lapidary cutting.

Geological facts

Chert and flint were among the first rocks utilized by early humans for toolmaking and starting fires via spark production with iron pyrite.

Field identification & locations

Identified by its extreme hardness (scratches glass readily), smooth shell-like conchoidal fracture surfaces, and fine-grained microcrystalline texture. Extremely common in limestone formations and river gravels worldwide.

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