sedimentary
Chert (Flint)
Chert (Cryptocrystalline Silicon Dioxide, SiO2)
Hardness: 6.5-7 Mohs; Color: Brown, tan, or grey; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Brown, tan, or grey
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Brown, tan, or grey; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed in marine environments through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation. Occurs as nodules or bedded deposits within limestone or chalk.
Uses & applications
Historically used for stone tools (arrowheads, knives) due to its sharp edges. Modernly used in construction aggregate and as a spark-generating material in survival gear.
Geological facts
Chert has been used by humans for over 2 million years. When struck against steel, it produces sparks, making it essential for early fire-starting and flintlock firearms.
Field identification & locations
Identify by its smooth, waxy feel and shell-like (conchoidal) fractures. It is commonly found in gravel beds or weathering out of limestone cliffs. Often found as rounded pebbles on beaches.
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