sedimentary
Chert (Field Stone)
Chert (Silicon Dioxide, SiO2)
Hardness: 7 on Mohs scale; Color: Dull tan to grey with brownish staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Dull tan to grey with brownish staining
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Dull tan to grey with brownish staining; Luster: Waxy to dull; Structure: Cryptocrystalline; 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 or groundwater environments. This specimen appears weathered/water-worn.
Uses & applications
Historical use for stone tools and arrowheads; modern use in road gravel, decorative landscaping, and as a source of silica in glass manufacturing.
Geological facts
Chert is so hard it can create sparks when struck against steel. Due to its predictable fracture pattern, it was the primary material for prehistoric 'flint-knapping' tools.
Field identification & locations
Identify in the field by its superior hardness (cannot be scratched by a steel blade) and smooth, shell-like (conchoidal) breaks. Very common in riverbeds and limestone outcrops.
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