sedimentary

Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Brown, grey, or tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.

Hardness: 7 on Mohs scale
Color: Brown, grey, or tan
Luster: Waxy to dull

Identified June 19, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Brown, grey, or tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.

Formation & geological history

Formed by the accumulation of siliceous remains of organisms (like diatoms or radiolarians) or chemical precipitation from silica-rich fluids in sedimentary basins. Primarily found in limestone or chalk beds.

Uses & applications

Used historically for stone tools and arrowheads due to its sharp edges; modernly used as a decorative stone, in road surfacing, or as flint for fire-starting.

Geological facts

Chert has been used by humans for hundreds of thousands of years to create weapons and tools. When struck, it produces a very predictable shell-like (conchoidal) fracture pattern.

Field identification & locations

Identify in the field by its hardness (scratches glass), waxy luster, and conchoidal fractures. Commonly found in riverbeds or as nodules within limestone outcrops.