sedimentary
Chert (Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Brownish-gold, tan, and cream-white. Luster: Dull to waxy. Crystal Structure: Trigonal (microcrystalline/cryptocrystalline). Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Brownish-gold, tan, and cream-white
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Brownish-gold, tan, and cream-white. Luster: Dull to waxy. Crystal Structure: Trigonal (microcrystalline/cryptocrystalline). Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation within sedimentary rock layers like limestone. Most terrestrial chert is hundreds of millions of years old.
Uses & applications
Historically used for making stone tools due to conchoidal fracturing. Modernly used in landscaping, as a gemstone (Jasper varieties), and crushed for aggregate.
Geological facts
Chert is so hard it can strike sparks against steel. It is often found as nodules within limestone or dolomite beds.
Field identification & locations
Identify by its 'waxy' texture when wet and characteristic conchoidal (shell-like) fracture patterns. Frequently found in riverbeds or eroded out of limestone outcrops.
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