sedimentary
Chert (Common Variety, Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Tan, brown, and grey banding; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Tan, brown, and grey banding
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Tan, brown, and grey banding; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed primarily as a chemical precipitate from silica-rich fluids or the accumulation of siliceous skeletal remains (diatoms, radiolarians) in marine environments. This specimen appears water-worn, likely from a fluvial (river) deposit.
Uses & applications
Used historically for stone tools and arrowheads due to its sharp fracture; currently used in construction as aggregate and as a low-cost lapidary material for tumbling.
Geological facts
Chert has been used by humans for over 2 million years. Its waxy texture and ability to produce razor-sharp edges made it the primary material for the Stone Age tool industry.
Field identification & locations
Identify in the field by its hardness (will scratch glass), waxy appearance, and smooth, curved (conchoidal) fractures. Often found in riverbeds or as nodules within limestone formations.
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