sedimentary
Chert / Chalcedony Nodules
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Tan, beige, brown; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Conchoidal fracture; Specific gravity: 2.6-2.65.
- Hardness
- 6
- Color
- Tan, beige, brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Tan, beige, brown; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Conchoidal fracture; Specific gravity: 2.6-2.65.
Formation & geological history
Formed by the precipitation of silica from groundwater or within sedimentary rock layers like limestone or chalk. Often accumulates in nodules during the diagenesis of oceanic sediments.
Uses & applications
Historically used for stone tools and arrowheads; currently used in jewelry (as agate or jasper variants), as landscape stone, or as a source for high-purity silica.
Geological facts
Chert was one of the first materials used by early humans to create sharp tools due to its conchoidal fracture pattern. It is highly resistant to chemical weathering.
Field identification & locations
Identify by its extreme hardness (will scratch glass), waxy feel, and smooth, curved (conchoidal) breakage. Commonly found in riverbeds or eroding out of limestone cliffs.
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