sedimentary
Chert (Cherty Flint)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-tan to light brown; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Grayish-tan to light brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-tan to light brown; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments. Often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges when broken. Today used in construction aggregate and as a collector's specimen.
Geological facts
Chert has been used by humans for millions of years to create tools. It is highly resistant to weathering, which is why it often remains as pebbles in stream beds after the surrounding limestone has eroded.
Field identification & locations
Identify by its very hard surface (scratches glass), waxy feel, and conchoidal (shell-like) fracture patterns. Found globally in sedimentary basins. Collectors look for unique colors or biological inclusions.
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