sedimentary
Chert (Flint)
Chert (Microcrystalline Quartz, SiO2)
Hardness: 7 (Mohs scale); Color: Gray, brown, and tannish-red; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Gray, brown, and tannish-red
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, brown, and tannish-red; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed via the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. This specimen shows typical waxy texture of microcrystalline quartz.
Uses & applications
Historically used for stone tools (arrowheads) due to sharp edges; currently used for road surfacing, decorative landscaping, and as fire-starting flint.
Geological facts
Chert is so hard it can scratch steel. When struck against steel, it produces sparks, which is why it was the primary material for flintlock firearms and early fire-starting kits.
Field identification & locations
Identify in the field by its waxy luster and conchoidal (shell-like) fracture patterns. Frequently found in limestone and chalk deposits as nodules.
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