sedimentary
Chert (Jasper/Flint variety)
Silicon dioxide (SiO2)
Hardness: 6.5-7 (Mohs); Color: Tan, brown, and cream; Luster: Waxy to dull; Structure: Cryptocrystalline (microscopic quartz crystals); Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Tan, brown, and cream
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Tan, brown, and cream; Luster: Waxy to dull; Structure: Cryptocrystalline (microscopic quartz crystals); Cleavage: None (conchoidal fracture).
Formation & geological history
Formed as a chemical precipitate or through the replacement of limestone/chalk by silica-rich fluids. Often found as nodules or pebbles in stream beds and coastal areas after millions of years of erosion.
Uses & applications
Historically used for stone tools and fire-starting (flint). Currently used in construction aggregate, as lapidary material for tumbling, and for specialized glass manufacturing.
Geological facts
Chert is so durable that it often survives long after the surrounding rock has eroded away. It was one of the first materials used by prehistoric humans to make arrowheads and scrapers due to its sharp edges when broken.
Field identification & locations
Identify by its 'waxy' texture and conchoidal (shell-like) fracture patterns. Frequently found in river beds, beaches, and gravel pits. It is harder than steel and will scratch a glass plate.
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