sedimentary
Chert (Jasper/Agate variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5–7 on Mohs scale. Color: Greenish-grey with iron staining. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Conchoidal fracture. Specific gravity: 2.65.
- Hardness
- 6
- Color
- Greenish-grey with iron staining
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5–7 on Mohs scale. Color: Greenish-grey with iron staining. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Conchoidal fracture. Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation in marine or groundwater environments. This specimen appears water-worn, smoothed by fluvial or coastal processes.
Uses & applications
Used historically for stone tools due to its sharp edges when fractured. Currently used in lapidary work, jewelry (decorative cabochons), and as landscaping stone.
Geological facts
Chert is so durable that it often survives long after the surrounding rock has weathered away. Ancient people used it extensively to create arrowheads, scrapers, and knives.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel nail) and smooth, shell-like conchoidal fracture. Commonly found in riverbeds, glacial tills, and coastal beaches.
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