sedimentary
Chert with Fossil inclusions
Microcrystalline Quartz (SiO2) with biogenic inclusions
Hardness: 7 Mohs; Color: Gray, tan, and cream; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Opaque.
- Hardness
- 7 Mohs
- Color
- Gray, tan, and cream
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 Mohs; Color: Gray, tan, and cream; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Opaque.
Formation & geological history
Formed in marine environments through the precipitation of silica or the accumulation of siliceous skeletal remains (like diatoms or radiolarians). Significant fossilization often occurs in the Paleozoic and Mesozoic eras.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers); currently used for road aggregate and as a collector's specimen if fossiliferous.
Geological facts
Chert is so durable that it often survives intense weathering that destroys surrounding limestone or chalk. It was one of the first materials used by early humans for fire-starting and weaponry.
Field identification & locations
Identify by its hardness (scratches glass), smooth waxy feel, and conchoidal (shell-like) fractures. Commonly found as nodules in limestone beds or as rounded pebbles in riverbeds and beaches.
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