sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs); Color: Dark grey to black; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture)
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Dark grey to black; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture)
Formation & geological history
Formed from the accumulation of silica-rich organic remains or chemical precipitation in marine or groundwater environments; common in limestone or chalk beds.
Uses & applications
Historically used for stone tools (knapping) and fire-starting; currently used in construction aggregate and as a collector specimen.
Geological facts
Flint was essential to early human survival for making sharp blades and spearheads because it fractures into extremely sharp edges.
Field identification & locations
Identified by its extremely smooth, shell-like (conchoidal) fracture surface and its ability to scratch glass. Commonly found as nodules in sedimentary rock layers.
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