sedimentary
Chert / Flint
Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: tan, grey, white; Luster: waxy to dull; Structure: microcrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- tan, grey, white
- Luster
- waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: tan, grey, white; Luster: waxy to dull; Structure: microcrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from groundwater within limestone or chalk beds.
Uses & applications
Historically used for stone tools and starting fires; currently used in construction aggregate, road metal, and occasionally as semi-precious gemstones.
Geological facts
Flint is a variety of chert that occurs in chalk or marly limestone. Because it breaks with very sharp edges, it was the primary material for prehistoric arrowheads and spear tips.
Field identification & locations
Identify by its waxy luster, extreme hardness (scratches glass), and shell-like (conchoidal) fracture patterns. Found globally in sedimentary rock outcrops and riverbeds.
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