sedimentary
Chert (Field Stone)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Dark brown to grey with tan bands; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: Conchoidal fracture
- Hardness
- 6
- Color
- Dark brown to grey with tan bands
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 Mohs; Color: Dark brown to grey with tan bands; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: Conchoidal fracture
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine environments; age varies by locality from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools and fire-starting (flint); currently used in decorative landscaping and as tumbling media for hobbyists.
Geological facts
Chert is so hard it can scratch steel and was the primary material for arrowheads and scrapers during the Stone Age due to its razor-sharp fracture edges.
Field identification & locations
Identify by its hardness, smooth waxy texture, and shell-like fracture pattern. Often found as nodules in limestone or as rounded river gravel.
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