sedimentary
Chert (Flint)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 7 on Mohs scale; Color: Tan, brown, or smoky grey; Luster: Waxy to vitreous; Crystal Structure: Trigonal (Microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, or smoky grey
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, or smoky grey; Luster: Waxy to vitreous; Crystal Structure: Trigonal (Microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the precipitation of silica from groundwater or the accumulation of silica-rich organic remains (like radiolarians or diatoms) in marine environments. It occurs often as nodules or bedded layers in limestone or chalk.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; industrially used as an abrasive, and in some jewelry as cabochons.
Geological facts
Chert has a distinctive conchoidal fracture, which means it breaks like glass, producing very sharp edges. This property made it the primary material for prehistoric survival tools globally.
Field identification & locations
Identify in the field by its smooth, waxy surface and the way it chips into sharp, curved flakes. It is frequently found in limestone outcrops or as rounded 'river rocks' in creek beds.
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