sedimentary
Chert (Jasper/Flint variety)
Microcrystalline silicon dioxide (SiO2)
Hardness: 7 Mohs scale; Color: Tan, brown, and grey mottled; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 Mohs scale
- Color
- Tan, brown, and grey mottled
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs scale; Color: Tan, brown, and grey mottled; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. This specific specimen appears to be a water-worn river cobble.
Uses & applications
Historically used for stone tools and weapons due to its sharp edges when broken. Currently used for landscaping, road aggregate, and as a lapidary material for polishing and jewelry.
Geological facts
Chert is so durable that it often survives long-distance transport in rivers and glacial deposits, which is why it is frequently found as rounded cobbles far from its original bedrock source.
Field identification & locations
Identify in the field by its hardness (it should scratch glass), waxy luster when wet, and distinctive conchoidal (shell-like) fracture patterns. Frequently found in riverbeds and gravel pits.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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