sedimentary
Chert Nodule (Flint)
Microcrystalline quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, white, or black; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, white, or black
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, white, or black; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed in sedimentary environments, specifically within limestone or chalk beds. It occurs as silica-rich fluids precipitate into cavities or replace organic material. These nodules often date back to the Cretaceous or Jurassic periods.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) and starting fires (striking steel). Modernly used in construction aggregate and as decorative landscaping stone.
Geological facts
Flint was one of the most important minerals for early humans, enabling the transition to advanced tool-making. When broken, it produces edges that can be sharper than a surgical steel scalpel.
Field identification & locations
Identify in the field by its distinct waxy, glass-like interior and a rough, white chalky outer 'rind' (cortex). It creates a sharp conchoidal fracture when struck. Commonly found in riverbeds or eroded limestone cliffs globally.
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