sedimentary
Chert (with inclusions)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Cream, grey, and tan with darker patches; Luster: Waxy to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Cream, grey, and tan with darker patches
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Cream, grey, and tan with darker patches; Luster: Waxy to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation from hydrothermal fluids in marine environments. This specimen appears water-worn, likely collected from a riverbed or beach.
Uses & applications
Historically used for stone tools (flintknapping) due to its sharp edges when broken. Today used as decorative gravel, in construction as road base, and by hobbyist collectors.
Geological facts
Chert is so durable that it can survive long periods of erosion, which is why it is often found as smooth pebbles in stream beds. Some cherts contain microscopic fossils. Darker varieties are often called flint.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its smooth, waxy feel and conchoidal (shell-like) fracture patterns. Frequently found in limestone and dolomite formations worldwide.
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