sedimentary
Chert (Yellow/Tan variety)
Microcrystalline or cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Tan, yellow-brown, or butterscotch; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Tan, yellow-brown, or butterscotch
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, yellow-brown, or butterscotch; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the precipitation of silica from groundwater or within deep-sea marine environments where silica-rich organisms (like radiolarians) accumulate and recrystallize. Often found in limestone or chalk beds.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; modern uses include road construction aggregate and decorative garden stones.
Geological facts
Chert is so hard it can create sparks when struck against steel, which made it a critical material for 'flintlock' firearms and ancient fire-starting techniques.
Field identification & locations
Identify in the field by its smooth, waxy texture and characteristic 'shell-like' (conchoidal) curved breaks. It cannot be scratched by a steel knife. Commonly found in riverbeds and eroded limestone outcrops.
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