sedimentary

Chert (often called Flint or River Stone)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Gray, tan, white, and mottled brown; Luster: Dull to waxy; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Gray, tan, white, and mottled brown
Luster: Dull to waxy

Identified June 21, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Gray, tan, white, and mottled brown; Luster: Dull to waxy; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. This specimen shows water-worn rounded edges, indicating it was transported by a river or stream.

Uses & applications

Historically used for stone tools and starting fires; currently used in road construction, landscaping, and occasionally as an abrasive.

Geological facts

Chert is so hard that it can scratch glass and steel. It was one of the most important materials for prehistoric humans to create sharp-edged tools like arrowheads and knives.