sedimentary
Chert (White-Grey variety)
Microcrystalline or cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: light grey to white; Luster: waxy to dull; Crystal structure: trigonal (microscopic); Cleavage: none (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- light grey to white
- Luster
- waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: light grey to white; Luster: waxy to dull; Crystal structure: trigonal (microscopic); 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. Can be found in nodules within limestone or chalk beds of various geological ages, frequently Paleozoic or Mesozoic.
Uses & applications
Historically used for stone tools (flintknapping) due to its sharp edges. Modernly used as road aggregate, architectural stone, and occasionally in jewelry as tumbled stones.
Geological facts
Chert is so hard it can scratch glass. It is chemically identical to quartz and amethyst but differs in its microscopic crystal structure. Ancient civilizations extensively traded high-quality chert for arrowheads and scrapers.
Field identification & locations
Identify by its 'flint-like' conchoidal (shell-like) fracture and extreme hardness. Commonly found in riverbeds, gravel pits, and areas with limestone outcroppings. To test in the field, see if it can scratch a steel knife blade.
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