sedimentary
Chert (Jasper/Iron-stained Quartzite)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Brown, tan, and reddish-orange due to iron oxide staining; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Brown, tan, and reddish-orange due to iron oxide staining
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Brown, tan, and reddish-orange due to iron oxide staining; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the precipitation of silica from groundwater or the accumulation of silica-rich organic remains (like radiolarians) in marine environments. This specific specimen appears water-worn, suggesting it was transport by a river or stream over thousands of years.
Uses & applications
Historically used for making stone tools (arrowheads/scrapers) due to its sharp edges when broken. Today, used as landscaping stone, in construction aggregate, or as lapidary material for tumbling and cabochons.
Geological facts
Chert is so durable it often survives long after the surrounding rock has eroded away. Because it is harder than steel, it was famously used as 'flint' in flintlock firearms to create sparks.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), its smooth 'waxy' texture compared to surrounding rocks, and its shell-like (conchoidal) fracture pattern. Found globally in riverbeds, glacial tills, and sedimentary outcrops.
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