sedimentary
Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Tan, brown, or buff; Luster: Dull to waxy; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Tan, brown, or buff
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, brown, or buff; Luster: Dull to waxy; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed in marine environments through the replacement of limestone or the accumulation of siliceous remains of diatoms or radiolarians. Often found as nodules or bedded layers.
Uses & applications
Historically used for stone tools and arrowheads; currently used in construction aggregate and as a collector's specimen.
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture produces extremely sharp edges for cutting tools and fire-starting.
Field identification & locations
Identify by its hardness (scratches glass), waxy luster on fresh breaks, and smooth, curved (conchoidal) fracture surfaces. Common in limestone outcrops.
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