sedimentary
Chert (Jasper)
Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Brownish-red to tan. Luster: Waxy to dull. Crystal structure: Trigonal (microscopic). Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Brownish-red to tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Brownish-red to tan. Luster: Waxy to dull. Crystal structure: Trigonal (microscopic). Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
Formation & geological history
Formed from the accumulation of silica-rich organic remains or chemical precipitation in marine environments. Often found in nodules within limestone or as bedded deposits.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges. Modern uses include decorative gravel, jewelry (cabochons), and lapidary art.
Geological facts
Chert has been used by humans for millions of years to make arrowheads and scrapers. Its fracture pattern allows it to be shaped into razor-sharp edges.
Field identification & locations
Identify in the field by its smooth, glass-like fracture and inability to be scratched by a steel knife. Common in sedimentary basins and riverbeds.
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