sedimentary
Chert (Jasper/Quartzite)
Microcrystalline Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Tan, yellow-orange, and grey banded; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Tan, yellow-orange, and grey banded
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, yellow-orange, and grey banded; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or chemical precipitation from groundwater within sedimentary layers. This rounded specimen suggests mechanical weathering in a river or beach environment.
Uses & applications
Historically used for making stone tools (arrowheads). Modern uses include landscaping, tumbling for collectors, and as an industrial abrasive.
Geological facts
Chert is so hard it can strike sparks against steel. It is one of the most durable rocks, often outlasting the surrounding bedrock in which it originally formed.
Field identification & locations
Identify by its 'waxy' texture and the way it breaks into sharp, curved edges (conchoidal fracture). It cannot be scratched by a steel knife. Common in riverbeds and gravel deposits worldwide.
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