sedimentary
Chert Nodules (with Flint core)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs; Color: White exterior (cortex) with tan/grey interior; Luster: Waxy to dull; Structure: Cryptocrystalline; Conchoidal fracture.
- Hardness
- 7 Mohs
- Color
- White exterior (cortex) with tan/grey interior
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs; Color: White exterior (cortex) with tan/grey interior; Luster: Waxy to dull; Structure: Cryptocrystalline; Conchoidal fracture.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) in seafloor sediments, eventually replacing carbonate material in limestone or chalk beds.
Uses & applications
Historically used for making stone tools (lithics) and starting fires; currently used for decorative stones, landscaping, and as a source of abrasive silica.
Geological facts
Flint and chert have been used for over 2 million years by early humans. This specimen shows a classic white 'cortex' which is a weathered outer layer of the silicious nodule.
Field identification & locations
Identified by its extremely smooth, waxy interior surface and its sharp, shell-like (conchoidal) breaking pattern. Found frequently in chalk outcrops or as river/beach pebbles.
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