sedimentary
Chert (Flint Nodules)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, brown with a white weathered cortex; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, brown with a white weathered cortex
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, brown with a white weathered cortex; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed by the accumulation of silica-rich organic remains (like sponge spicules or radiolarians) or chemical precipitation in marine environments, often replacing carbonate material in limestone or chalk.
Uses & applications
Historically used for stone tools and weapons (arrowheads); currently used in road construction, as jewelry (when patterned), and as flint for spark-striking.
Geological facts
Chert and flint are among the oldest materials used by humans for tool-making due to their predictable fracturing; they can create edges sharper than a steel scalpel.
Field identification & locations
Identify by its waxy luster, extreme hardness (it will scratch glass), and its characteristic shell-like (conchoidal) fracture patterns. Found globally in limestone formations and on beaches/riverbeds near such deposits.
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