sedimentary
Chert (Pink variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Pink, tan, or reddish; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 6
- Color
- Pink, tan, or reddish
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Pink, tan, or reddish; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (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 from silica-rich fluids within other sedimentary rocks like limestone. Common in Paleozoic to Cenozoic strata.
Uses & applications
Historically used for stone tools and weapons due to sharp edges; currently used for landscaping, road ballast, and sometimes as semi-precious gemstones for jewelry (cabochons).
Geological facts
Chert is so hard it can strike sparks from steel, which led to its historical use as 'flint' for starting fires and in flintlock firearms. Pink varieties often get their color from trace amounts of iron oxide.
Field identification & locations
Identify by its 'flint-like' behavior: it breaks with smooth, curved surfaces (conchoidal fracture) and cannot be scratched by a steel knife. Commonly found in riverbeds, gravel pits, and as nodules in limestone outcrops.
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