sedimentary

Chert (specifically Jaspery Chert)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Reddish-brown to tan; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Reddish-brown to tan
Luster: Dull to waxy

Identified July 8, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Reddish-brown to tan; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed primarily through the chemical precipitation of silica or the accumulation of silica-rich organic debris (like radiolarians) on the ocean floor, followed by diagenesis.

Uses & applications

Historically used for stone tools (arrowheads) due to conchoidal fracturing; used today as decorative stones, in landscaping, and as lapidary material.

Geological facts

Chert is so hard it can strike sparks from steel, which led to its historical use as flint. This specimen shows the characteristic waxy luster and sharp, jagged edges typical of microcrystalline silica.

Field identification & locations

Identify in the field by its hardness (cannot be scratched by a steel knife), its smooth shell-like (conchoidal) fracture, and its lack of visible grains. Common in limestone and chalk formations.