sedimentary
Chert (Iron-rich River Pebble)
Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs. Color: Dull brown to reddish-brown (likely due to iron oxide staining). Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
- Hardness
- 6
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs. Color: Dull brown to reddish-brown (likely due to iron oxide staining). Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
Formation & geological history
Formed from the accumulation of microscopic silica-rich organisms or chemical precipitation. This specific piece has been water-worn into a smooth pebble shape in a fluvial (river) environment, likely over thousands of years.
Uses & applications
Primarily used as decorative stone in landscaping or river rock; historically used for stone tools like scrapers and arrowheads due to its conchoidal fracture.
Geological facts
Chert is so durable that it often survives as a pebble long after the original parent rock has weathered away. It is closely related to flint, jasper, and agate.
Field identification & locations
Identify in the field by its hardness (will scratch glass) and smooth, rounded water-worn texture. Commonly found in riverbeds, gravel pits, and coastal areas throughout North America and Europe.
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