sedimentary
Chert (Jasper/Quartzite variant)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 Mohs; Color: Gray, tan, with reddish-brown iron oxide banding; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Gray, tan, with reddish-brown iron oxide banding
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Gray, tan, with reddish-brown iron oxide banding; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich microfossils or chemical precipitation within sedimentary layers, then smoothed by water erosion through river or glacial transport.
Uses & applications
Historically used for stone tools due to its sharp edges; currently used for landscaping, road aggregate, and as a common tumbling rock for hobbyists.
Geological facts
Chert was one of the most important minerals for early humans, used for making arrowheads and scraping tools because it breaks with incredibly sharp, predictable edges.
Field identification & locations
Commonly found in riverbeds, beaches, and glacial till. Identify in the field by its hardness (will scratch glass) and its smooth, rounded appearance when found as a river stone.
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