sedimentary
Chert (Flint / Jasper)
Microcrystalline Quartz (SiO2) with Iron Oxide inclusions
Hardness: 7 on Mohs scale. Color: Brownish-yellow, tan, with black/dark iron oxide staining. Luster: Dull to waxy. Fracture: Conchoidal to sub-conchoidal. Cleavage: None. Specific Gravity: ~2.65.
- Hardness
- 7 on Mohs scale
- Color
- Brownish-yellow, tan, with black/dark iron oxide staining
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale. Color: Brownish-yellow, tan, with black/dark iron oxide staining. Luster: Dull to waxy. Fracture: Conchoidal to sub-conchoidal. Cleavage: None. Specific Gravity: ~2.65.
Formation & geological history
Formed via the accumulation and precipitation of microcrystalline silica, often in marine or limnic environments, or through secondary silica replacement in limestone or chalk beds. Iron oxides account for the yellow-brown color.
Uses & applications
Historically used for knapping stone tools, arrowheads, and spark-striking flintlocks. Currently used in road aggregate, decorative gravel, and lapidary work.
Geological facts
Chert and flint were among the most critical resources for early humans due to their ability to produce extremely sharp edges when fractured along conchoidal break lines.
Field identification & locations
Identified by its hardness (scratches glass readily), smooth or waxy texture, and sharp curved fractures. Widely distributed in river gravels, limestone outcrops, and glacial deposits worldwide.
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