sedimentary
Chert (Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Yellowish-brown with dark inclusions; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Yellowish-brown with dark inclusions
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Yellowish-brown with dark inclusions; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Forms through the precipitation of silica from groundwater or the accumulation of silica-rich microfossils. Often found as nodules within limestone or as bedded deposits.
Uses & applications
Used historically for stone tools and arrowheads; today used as decorative garden stones, in jewelry (lapidary), and as a minor abrasive.
Geological facts
Chert is so hard it can scratch steel. This specific variety with yellow-brown hues is often referred to locally as yellow jasper or river chert.
Field identification & locations
Identified by its extreme hardness, waxy feel when smooth, and sharp conchoidal (shell-like) edges when broken. Extremely common in riverbeds and gravel pits.
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