sedimentary
Chert (or Microcrystalline Quartz)
Chert (Silicon Dioxide, SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, or off-white; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, or off-white
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, or off-white; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation in saltwater environments. Often found as nodules within limestone or shale beds.
Uses & applications
Historically used for making stone tools due to its conchoidal fracture (sharp edges). Modern uses include construction aggregate, road surfacing, and decorative landscaping rock.
Geological facts
Chert is so hard it can strike sparks against steel, a property that led to its use in flintlock firearms. 'Flint' is actually just a dark-colored variety of chert.
Field identification & locations
Look for a smooth, waxy texture and edges that break like thick glass (conchoidal fracture). It is frequently found in riverbeds or eroded out of limestone cliffs. Collectors value 'omars' or specifically shaped nodules.
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