sedimentary
Chert (and Jasper variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Tan, brown, and grey; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 6
- Color
- Tan, brown, and grey
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Tan, brown, and grey; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary basins. It often occurs as nodules within limestone or chalk, replacing original carbonate material over millions of years.
Uses & applications
Historically used for stone tools and arrowheads due to its sharp fracture edges. Today it is used in road construction as aggregate, in jewelry (when decorative like jasper), and as a specimen for geological study.
Geological facts
Chert was one of the most important raw materials for early humans because its conchoidal fracture allows it to be shaped into razor-sharp tools. It is highly resistant to chemical weathering.
Field identification & locations
Identify by its waxy luster, smoothness, and 'shell-like' conchoidal fracture patterns. It will scratch glass and won't react with acid. Commonly found in limestone outcrops or as river-worn pebbles.
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