sedimentary

Chert (variations include Flint/Jasper)

Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Brown, reddish-brown, tan, or grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic crystals); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 6
Color: Brown, reddish-brown, tan, or grey
Luster: Waxy to dull

Identified March 31, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich microfossils (like radiolarians or diatoms) or via chemical precipitation in limestone/chalk beds. It can span from the Precambrian to recent geological ages.

Uses & applications

Historically used for stone tools (knapping) and fire-starting. Currently used in road surfacing, as abrasive material, and sometimes in jewelry (as jasper/agate).

Geological facts

Chert has a conchoidal fracture, allowing it to break into sharp edges, which made it the primary material for prehistoric arrowheads and spear tips. It is extremely chemically stable and resistant to weathering.

Field identification & locations

Identify in the field by its smooth, waxy surface and characteristic shell-like (conchoidal) fracture patterns when broken. It cannot be scratched by a steel knife. Common in riverbeds and limestone outcrops.