sedimentary

Chert Pebble (Jasper or Agate variety)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: tan, brown, and reddish-brown with mottled patterns; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7.

Hardness: 6
Color: tan, brown, and reddish-brown with mottled patterns
Luster: waxy to dull

Identified July 8, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed via the accumulation of silica-rich fluids in sedimentary environments or by the replacement of carbonate rocks. This specimen is a rounded river or beach pebble, smoothed by water erosion.

Uses & applications

Tumbled for decorative use, lapidary work, used historically for stone tools due to sharp fracture edges, and used in landscaping.

Geological facts

Chert is one of the most common materials used by early humans for making arrowheads and scrapers. Its toughness and hardness make it very resistant to weathering.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), waxy texture when broken, and lack of visible grains. Found globally in riverbeds, glacial tills, and coastal deposits.

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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