sedimentary

Chert (specifically Jasper or Flint variant)

Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, reddish-yellow; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Brown, tan, reddish-yellow
Luster: Dull to waxy

Identified February 19, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, reddish-yellow; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & geological history

Formed as nodules or beds in limestone or chalk through the accumulation of silica-rich microfossils or chemical precipitation from groundwater. It can range in age from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools/arrowheads due to sharp edges; currently used for landscaping, road aggregate, and sometimes as a minor gemstone for lapidary work.

Geological facts

Chert was one of the most important minerals to prehistoric humans because its conchoidal fracture allows it to be shaped into razor-sharp blades and points.

Field identification & locations

Identify by its 'shell-like' conchoidal fracture patterns and inability to be scratched by a steel knife. Frequently found in riverbeds, gravel pits, and desert pavement.