sedimentary

Chert

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Tan, beige, or cream; Luster: Dull to waxy; Crystal structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.5-2.8.

Hardness: 6
Color: Tan, beige, or cream
Luster: Dull to waxy

Identified June 15, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Tan, beige, or cream; Luster: Dull to waxy; Crystal structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.5-2.8.

Formation & geological history

Formed primarily in marine environments where silica-rich fluids replace organic material or precipitate from solution. Found in beds or nodules within limestone or chalk.

Uses & applications

Historically used for stone tools (arrowheads). Modern uses include road surfacing, decorative landscaping, and as a polishing media.

Geological facts

Chert has a distinct conchoidal fracture that creates very sharp edges, leading to its extensive use by prehistoric humans for hunting tools and fire-starting.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like fracture surfaces. Often found in riverbeds or as nodules weathering out of limestone cliffs.