sedimentary

Chert (Arrowhead Fragment)

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale); Color: Gray, brown, and translucent tan; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Gray, brown, and translucent tan
Luster: Waxy to vitreous

Identified July 6, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. Specimen shows evidence of anthropogenic knapping (flake scars) indicative of stone tool manufacturing.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers, knives) due to its sharp conchoidal fracture. Currently valued as an archaeological artifact and for lapidary use.

Geological facts

Chert was one of the most important minerals for early humans. This specimen appears to be a bifacially worked fragment or a large percussion flake from a lithic reduction process.

Field identification & locations

Identify in the field by its waxy texture, inability to be scratched by steel, and sharp, shell-like (conchoidal) fracture points. Commonly found in limestone and chalk formations.

Other sedimentary specimens

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Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

sedimentary

Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

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Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary

Sandstone

Arenite (primarily SiO2)

sedimentary