sedimentary
Chert Pebble (Yellow/Brown Jasper variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Yellow-brown, tan, or ochre; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 6
- Color
- Yellow-brown, tan, or ochre
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Yellow-brown, tan, or ochre; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the precipitation of silica in sedimentary environments, often as nodules in limestone or chalk beds. This specific specimen has been water-worn into a rounded pebble, showing age through environmental erosion.
Uses & applications
Historically used for making stone tools (flintknapping); currently used in decorative gravel, lapidary work (tumbling/polishing), and as a common component in stream beds.
Geological facts
Chert and Jasper are essentially the same material chemically; Jasper specifically refers to the opaque, colored varieties (often from iron oxides). It is one of the most durable and common stones found in riverbeds worldwide.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its smooth, waxy feel. It is commonly found in gravel pits, riverbanks, and beaches. Collectors look for unique banding or patterns.
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