sedimentary

Chert (Jasper/Chalcedony)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Tan, brown, and yellowish-orange with waxy luster; Crystal Structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Tan, brown, and yellowish-orange with waxy luster

Identified July 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (such as diatoms or radiolarians) or chemical precipitation from hydrothermal fluids. This process typically occurs in deep-sea environments or as replacement nodules in limestone and chalk.

Uses & applications

Historically used for stone tools due to its sharp conchoidal fracture. Modern uses include decorative landscaping, flint-knapping for hobbyists, and as a source of silica in glass manufacturing.

Geological facts

Chert is so hard that it can scratch steel and produce sparks when struck against iron, making it a primary material for fire-starting throughout human history. This specimen shows typical 'waxy' texture and iron oxide staining.

Field identification & locations

Identify in the field by its smooth, shell-like fracture surfaces and extreme hardness. Look for it in riverbeds or as nodules protruding from weathered limestone outcrops. Common worldwide, especially in the central and western United States.

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Brown Sandstone (River Rock)

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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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Shale or Slaty Mudstone

Argillaceous sedimentary rock

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