sedimentary
Chert (and/or Siltstone River Pebble)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 6.5-7 on Mohs scale. Color: Gray, brownish-green. Luster: Dull to waxy. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
- Hardness
- 6
- Color
- Gray, brownish-green
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Gray, brownish-green. Luster: Dull to waxy. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich marine organisms or chemical precipitation from groundwater within sedimentary layers. This specific specimen appears to be a stream-worn pebble, likely from the Paleozoic or Mesozoic era.
Uses & applications
Historically used for stone tools (arrowheads). Modern uses include road aggregate, decorative landscaping, and occasionally lapidary work if the color is unique.
Geological facts
Chert is so durable that it often survives long after the surrounding rock has eroded away. It is essentially a non-gemstone version of jasper or flint.
Field identification & locations
Identify by its hardness (it will scratch glass) and smooth, water-worn exterior. Found commonly in riverbeds and gravel pits. Collectors look for unique shapes or colors.
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