sedimentary
Chert (River Stone)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Gray, tan, brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5-2.8
- Hardness
- 6
- Color
- Gray, tan, brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Gray, tan, brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5-2.8
Formation & geological history
Formed via the accumulation of silica-rich microfossils (like radiolaria or diatoms) or chemical precipitation from groundwater within sedimentary layers. This specimen has been naturally tumbled and rounded by water action.
Uses & applications
Historically used for making stone tools (arrowheads/scrapers); currently used as decorative landscaping stone, aggregate in construction, and for tumbling/collecting.
Geological facts
Chert is essentially a non-banded form of chalcedony. It was one of the most important minerals for early humans because its conchoidal fracture produces extremely sharp edges.
Field identification & locations
Identify by its waxy luster, smoothness, and the way it breaks into curved, glass-like shards (conchoidal fracture). Commonly found in riverbeds, beaches, and limestone outcrops globally.
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