sedimentary

Chert (Jasper/Agate variety)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 Mohs; Color: Tan, brown, white, and translucent gray; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 6
Color: Tan, brown, white, and translucent gray
Luster: Waxy to vitreous

Identified May 16, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of siliceous remains of organisms or chemical precipitation from silica-rich fluids in sedimentary basins. This specimen appears to have brecciated or replacement textures common in hydrothermal environments.

Uses & applications

Historically used for stone tools (knapping) due to sharp edges; currently used for lapidary work, cabochons, landscaping, and as a collector's specimen.

Geological facts

Chert was one of the most vital materials for early humans to create arrowheads and scrapers. Some varieties containing fossils are known as 'fossiliferous chert'.

Field identification & locations

Identify by its 'flint-like' waxy appearance and shell-like (conchoidal) fractures. It will easily scratch glass. Found globally in limestone formations and river gravel beds.

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Sandstone or Siltstone

Arenite (if sandstone)

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Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

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Shale or Slaty Mudstone

Argillaceous sedimentary rock

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Sandstone

Arenite (primarily SiO2)

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