sedimentary
Chert / Flint
Silicon Dioxide (SiO₂)
Hardness: 7 on Mohs scale; Color: typically gray, white, or brown; Luster: waxy to dull; Crystal structure: cryptocrystalline (microscopic quartz); Cleavage: none (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- typically gray, white, or brown
- Luster
- waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically gray, white, or brown; Luster: waxy to dull; Crystal structure: cryptocrystalline (microscopic quartz); 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 chemical precipitation from groundwater within limestone or chalk beds. Often found in Phanerozoic age strata.
Uses & applications
Historically used for stone tools and weapons (arrowheads). Modern uses include road surfacing, flintlock mechanisms, and as decorative gemstones (jasper).
Geological facts
Chert has been used by humans for over 2 million years. When struck against steel, it creates sparks, which made it the primary ignition source for early firearms and survival tools.
Field identification & locations
Identify by its characteristic conchoidal fracture (smooth, curved surfaces like broken glass) and its ability to scratch glass. Commonly found in stream beds or eroding out of limestone outcrops.
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