sedimentary
Chert (likely Flint)
Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Dark brown to black; Luster: Waxy to vitreous; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Dark brown to black
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Dark brown to black; Luster: Waxy to vitreous; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed primarily through the chemical precipitation of silica-rich fluids within sedimentary environments. These often originate from the accumulation of silica-based biological remains like sponge spicules or radiolarians, typically found in limestone or chalk beds.
Uses & applications
Historically used for stone tools and starting fires; currently used in construction as aggregate, in ball mills, and sometimes as a minor gemstone or landscaping stone.
Geological facts
Flint was arguably the most important resource for prehistoric humans, used to create razor-sharp edges for hunting. It sparks when struck against steel due to its hardness and chemical composition.
Field identification & locations
Identified in the field by its smooth, waxy texture and characteristic conchoidal (shell-like) fractures. It is commonly found in riverbeds or within chalk/limestone outcrops. Collect near limestone regions globally.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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