sedimentary
Chert Nodules in Limestone
Microcrystalline Quartz (SiO2) within Calcium Carbonate (CaCO3)
Hardness: 7 (inner chert), 3 (outer limestone); Color: Creamy tan to white; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture in centers)
- Hardness
- 7 (inner chert), 3 (outer limestone)
- Color
- Creamy tan to white
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (inner chert), 3 (outer limestone); Color: Creamy tan to white; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture in centers)
Formation & geological history
Formed through the precipitation of silica within limestone beds, often replacing organic material or filling voids in seafloor sediments over millions of years
Uses & applications
Historically used for stone tools (flint); currently used as specimens for geological study, decorative garden stones, and occasionally lapidary work
Geological facts
Chert is so durable that it often remains as 'river gravel' long after the surrounding limestone host rock has weathered away
Field identification & locations
Identified by the hard, waxy center surrounded by a softer, chalky 'cortex.' Found globally in sedimentary basins, particularly in areas with ancient seabed deposits
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