sedimentary
Chert (Jasper variety)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 on the Mohs scale. Color: Opaque tan, brown, and reddish tones. Luster: Waxy to dull. Crystal structure: Cryptocrystalline (microscopic quartz). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Opaque tan, brown, and reddish tones
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on the Mohs scale. Color: Opaque tan, brown, and reddish tones. Luster: Waxy to dull. Crystal structure: Cryptocrystalline (microscopic quartz). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or via chemical precipitation from silica-rich fluids within sedimentary rock layers. It is found in deposits ranging from Precambrian to recent times.
Uses & applications
Historically used for stone tools and weapons (arrowheads) due to its sharp edges. Modernly used as semi-precious gemstones in jewelry, lapidary art, and occasionally as industrial abrasives or decorative landscaping stone.
Geological facts
Chert was one of the first materials used by early humans to create fire by striking it against steel or pyrite. It is exceptionally durable and resistant to chemical weathering, often remaining after the surrounding host rock has eroded away.
Field identification & locations
Identify in the field by its conchoidal (shell-like) fracture, extreme hardness (it will scratch glass), and waxy texture. It is commonly found as nodules in limestone or as distinct bedded layers in marine sedimentary sequences.
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