sedimentary
Chert Pebble (Jasper variant)
Microcrystalline Quartz (SiO2)
Hardness: 6.5–7 on Mohs scale; Color: Dull olive-green to brownish-yellow; Luster: Waxy to vitreous when wet, dull when dry; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.7.
- Hardness
- 6
- Color
- Dull olive-green to brownish-yellow
- Luster
- Waxy to vitreous when wet, dull when dry
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Dull olive-green to brownish-yellow; Luster: Waxy to vitreous when wet, dull when dry; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.7.
Formation & geological history
Formed from the recrystallization of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments. This specimen has been rounded and smoothed via fluvial (river) or beach erosion over thousands to millions of years.
Uses & applications
Primarily used as decorative landscaping stone or river rock. Higher quality colorful variants are used in lapidary work (tumbling and cabochon cutting). Historically, chert was used for stone tools due to its sharp conchoidal edges.
Geological facts
Chert is so durable that it often survives long after the surrounding limestone or shale has eroded away. The green tint in many specimens is often caused by the presence of iron-bearing silicate minerals like chlorite or celadonite.
Field identification & locations
Identify in the field by its smoothness, lack of visible grains, and extreme hardness (it will scratch glass and steel). Common in riverbeds, glacial tills, and coastal beaches. Collectors should look for 'waxy' texture and interesting banding.
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