sedimentary
Chert (River Siltstone/Quartzite type)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (can scratch glass). Color: Gray-brown/olive tan. Luster: Waxy to sub-vitreous. Texture: Very smooth, likely water-worn. Structure: Cryptocrystalline.
- Hardness
- 6
- Color
- Gray-brown/olive tan
- Luster
- Waxy to sub-vitreous
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Physical properties
Hardness: 6.5-7 (can scratch glass). Color: Gray-brown/olive tan. Luster: Waxy to sub-vitreous. Texture: Very smooth, likely water-worn. Structure: Cryptocrystalline.
Formation & geological history
Formed via the accumulation of silica-rich organic remains or chemical precipitation in marine or freshwater environments. This specific specimen has been rounded and polished by fluvial (river) action over long periods.
Uses & applications
Historically used for making stone tools (arrowheads). Modern uses include landscaping, construction aggregate, and as 'river rocks' for decoration or aquarium use.
Geological facts
Chert is so durable that it often survives long after the surrounding rock has eroded away. It produces a spark when struck against steel, which made it vital for prehistoric fire-starting.
Field identification & locations
Identify by its smooth, waxy feel, conchoidal fracture (if chipped), and high hardness. Commonly found in riverbeds, glacial tills, and sedimentary basins worldwide.
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