sedimentary
Chert Nodule
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs scale; Color: Tan, beige, or gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 Mohs scale
- Color
- Tan, beige, or gray
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs scale; Color: Tan, beige, or gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed by the precipitation of silica within sedimentary layers (usually limestone or chalk) during diagenesis. They often form from the remains of silica-shelled organisms like radiolaria or diatoms.
Uses & applications
Historically used for making stone tools (arrowheads). Currently used in road construction as aggregate or as a decorative landscaping stone.
Geological facts
Chert nodules are chemically identical to flint, although 'flint' usually refers to dark gray/black varieties found specifically in chalk.
Field identification & locations
Identify by its smooth, waxy feel and distinctive shell-like (conchoidal) fracture pattern when broken. It cannot be scratched by a steel knife. Common in limestone outcrops.
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