sedimentary
Chert (Flint variety)
Chert (Cryptocrystalline Quartz, SiO2)
Hardness: 7 (Mohs scale). Color: Tan, beige, gray, and brown. Luster: Waxy to dull. Crystal structure: Hexagonal (microscopic). Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Tan, beige, gray, and brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale). Color: Tan, beige, gray, and brown. Luster: Waxy to dull. Crystal structure: Hexagonal (microscopic). Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in marine environments. Often found as nodules within limestone or chalk beds.
Uses & applications
Historically used for making stone tools and fire-starting. Currently used as road aggregate, in landscaping, and some varieties as gemstones (Jasper).
Geological facts
Because it breaks with a conchoidal fracture (smooth, curved surfaces), it can be knapped into extremely sharp edges, which is why it was the primary material for prehistoric arrowheads.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), waxy appearance on fresh breaks, and sharp edges. Extremely common in gravel pits and sedimentary outcrops globally.
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