sedimentary

Chert (with Limestone/Carbonate matrix)

Sedimentary cryptocrystalline silica (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs scale; Color: Gray, tan, and yellowish-brown; Luster: Waxy to dull/earthy; Crystal structure: Cryptocrystalline; Cleavage: None (has conchoidal fracture); Specific gravity: approx. 2.65

Hardness: 6
Color: Gray, tan, and yellowish-brown
Luster: Waxy to dull/earthy

Identified June 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation within marine limestone beds. Common in Paleozoic and Mesozoic sedimentary basins.

Uses & applications

Historically used for stone tools (arrowheads). Modernly used as road aggregate, in landscaping, and occasionally as a source of silica for industrial manufacturing.

Geological facts

Chert is so hard it can scratch glass and steel. High-quality varieties are known as flint. This specific specimen shows weathering rinds and potential secondary carbonate deposits.

Field identification & locations

Identify by its extreme hardness, waxy texture on fresh surfaces, and lack of visible grains. Often found as nodules or layers within limestone cliffs or in riverbeds after the softer limestone has eroded.