sedimentary
Chert (River Stone)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs scale; Color: Gray, brown, tan, and waxy; Luster: Dull to waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 Mohs scale
- Color
- Gray, brown, tan, and waxy
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 Mohs scale; Color: Gray, brown, tan, and waxy; Luster: Dull to waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed via the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation from groundwater. This specimen has been rounded and smoothed by water erosion in a river or beach environment.
Uses & applications
Historically used for stone tools (arrowheads). Currently used in decorative landscaping, construction aggregate, and as a polishing material for rock tumblers.
Geological facts
Chert and its variant, Flint, were among the first materials used by early humans to create fire and sharp tools due to their predictable conchoidal fracturing.
Field identification & locations
Identify in the field by its smooth, waxy feel, extreme hardness (it will scratch glass), and rounded 'river rock' shape. Found globally in riverbeds and sedimentary basins.
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