sedimentary

Chert Pebble

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Mottled gray, brown, and tan; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 7 on Mohs scale
Color: Mottled gray, brown, and tan
Luster: Waxy to dull

Identified April 6, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Mottled gray, brown, and tan; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & geological history

Formed primarily in marine environments where silica-rich fluids replace organic material or precipitate from water. Often found as nodules within limestone or as water-worn pebbles in stream beds.

Uses & applications

Historically used for making stone tools (arrowheads). Modernly used in construction aggregate, road base, and occasionally as tumbled pocket stones or for lapidary work.

Geological facts

Chert has been used by humans for millions of years due to its ability to fracture with extremely sharp edges. Flint is a well-known variety of dark chert.

Field identification & locations

Identify in the field by its hardness (will scratch glass), waxy appearance, and smooth, curved (conchoidal) fracture surfaces. Commonly found in riverbeds and gravel pits.