sedimentary

Chert (specifically Flint or Jasper variant)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Brown, tan, and dark translucent patches; Luster: Waxy to vitreous; Crystal Structure: Trigonal (cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Brown, tan, and dark translucent patches
Luster: Waxy to vitreous

Identified June 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic or chemical deposits in sedimentary environments. Often found as nodules in limestone or chalk beds. This specimen appears to have water-worn or weathered cortex.

Uses & applications

Historically used for stone tools (knapping) and fire-starting. Currently used as an abrasive, in decorative landscaping, or as a semi-precious gemstone when polished.

Geological facts

Chert was one of the most important lithic materials for prehistoric humans due to its predictable conchoidal fracturing, which allows for the creation of razor-sharp edges.

Field identification & locations

Identify by its waxy luster, hardness (can scratch glass), and shell-like (conchoidal) fractures on broken surfaces. Commonly found in riverbeds, gravel pits, and eroding out of limestone outcrops.

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)

sedimentary

Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

sedimentary

Chert Breccia

Brecciated Chert (Microcrystalline Silica)

sedimentary

Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary

Sandstone

Arenite (primarily SiO2)

sedimentary