sedimentary
Chert (Field Stone)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: tan, grey, cream; Luster: waxy to dull; Structure: microcrystalline; Fracture: conchoidal; Specific Gravity: 2.65
- Hardness
- 7 (Mohs scale), Color: tan, grey, cream
- Color
- tan, grey, cream
- Luster
- waxy to dull
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, grey, cream; Luster: waxy to dull; Structure: microcrystalline; Fracture: conchoidal; Specific Gravity: 2.65
Formation & geological history
Formed as nodules or beds in sedimentary rocks through the precipitation of silica. Common in North Dakota glacial drift and riverbeds.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges; used today as decorative gravel or industrial abrasive.
Geological facts
The location provided (Minot, ND area) is rich in chert and flint deposited by glaciation. Chert is extremely durable and can survive millions of years of transport by water or ice.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and smooth, shell-like (conchoidal) fracture surfaces.
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