sedimentary
Chert (Flint)
Microcrystalline or cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Grey, black, or brown; Luster: Waxy to dull; Crystal structure: Hexagonal (microscopic); Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Grey, black, or brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Grey, black, or brown; Luster: Waxy to dull; Crystal structure: Hexagonal (microscopic); Cleavage: None (conchoidal fracture).
Formation & geological history
Formed by the accumulation of silica-rich organic remains (like diatoms or radiolarians) or through chemical precipitation in marine environments. Common in limestone and chalk beds.
Uses & applications
Historically used for stone tools and fire-starting. Currently used in road surfacing and as a decorative stone in landscaping.
Geological facts
Chert has a conchoidal fracture, which means it breaks into sharp edges, making it the primary material for prehistoric arrowheads and spear points.
Field identification & locations
Identify by its waxy texture, great hardness (scratches glass), and distinctive shell-like (conchoidal) curved breakage patterns. Found globally in sedimentary basins.
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