sedimentary

Chert (often called Jasper in this color variety)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Tan, brown, and reddish due to iron oxide; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 6
Color: Tan, brown, and reddish due to iron oxide
Luster: Waxy to dull

Identified May 8, 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. Common in marine limestone formations where it replaces carbonate minerals over millions of years.

Uses & applications

Historically used for stone tools and arrowheads due to sharp fractures; currently used for decorative purposes, landscape gravel, and semi-precious jewelry (as Jasper).

Geological facts

Chert was one of the first materials used by early humans for fire-starting and tool-making because it breaks into sharp, glass-like edges. It is incredibly durable and resists chemical weathering.

Field identification & locations

Identify by its waxy luster, extreme hardness (scratches glass), and distinctive shell-like (conchoidal) fracture patterns. Found globally in riverbeds, glacial till, and embedded in limestone cliffs.

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