sedimentary

Chert (Jasper-like Siliceous Rock)

Chert (Silicon Dioxide, SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Opaque brown, yellow, and grayish-green; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 6
Color: Opaque brown, yellow, and grayish-green
Luster: Waxy to dull

Identified July 8, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich microfossils (like radiolarians or diatoms) or by chemical precipitation in sedimentary basins. This specimen shows signs of stream tumbling, smoothing its edges over time.

Uses & applications

Used historically for stone tools due to its conchoidal fracture. Modernly used in landscaping, as aquarium decor, or tumbled for lapidary hobbies.

Geological facts

Chert is so durable that it often survives long after the surrounding rock has weathered away. Similar varieties like Jasper are prized for their vibrant patterns caused by iron impurities.

Field identification & locations

Identify by its hardness (it will scratch glass) and its smooth, waxy feel. Often found in riverbeds or gravel pits as rounded pebbles. Collectors look for unique color patterns.

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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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Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Shale or Slaty Mudstone

Argillaceous sedimentary rock

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Sandstone

Arenite (primarily SiO2)

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