sedimentary
Chert (Jasper-bearing)
Chert (Silicon Dioxide, SiO2)
Hardness: 7 (Mohs scale); Color: Variegated greens, grays, and reddish-browns (iron-stained); Luster: Waxy to dull (on weathered surfaces); Crystal structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6 – 2.7.
- Hardness
- 7 (Mohs scale)
- Color
- Variegated greens, grays, and reddish-browns (iron-stained)
- Luster
- Waxy to dull (on weathered surfaces)
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Physical properties
Hardness: 7 (Mohs scale); Color: Variegated greens, grays, and reddish-browns (iron-stained); Luster: Waxy to dull (on weathered surfaces); Crystal structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6 – 2.7.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater. This specimen appears weathered and may have been part of a larger formation dating from the Precambrian to Cenozoic eras.
Uses & applications
Historically used for stone tools (arrowheads/scrapers) due to conchoidal fracture. Modern uses include landscaping, construction aggregate, and lapidary work (when colorful like Jasper).
Geological facts
Chert is so durable that it often remains as 'residual' rock after surrounding limestone has weathered away. The reddish patches in this specimen are likely Jasper, a variety of chert colored by iron impurities.
Field identification & locations
Identify by its extreme hardness (scratches glass), waxy feel on fresh breaks, and curved 'conchoidal' fracture patterns. Common globally in sedimentary basins. Look for it in riverbeds or as 'nodules' in limestone outcrops.
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