sedimentary
Chert (Flint)
Chert (SiO2)
Hardness: 7 on Mohs scale; Color: Yellowish-brown, tan, and dark gray; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Yellowish-brown, tan, and dark gray
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Yellowish-brown, tan, and dark gray; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine environments. Often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools and weapons (arrowheads). Today used in road construction, as jewelry (when patterned), and occasionally for fire-starting in flintlock mechanisms.
Geological facts
Chert is so hard it can scratch glass. It has been used by humans for over 2 million years to create sharp edges. It is chemically identical to quartz but has a different internal structure.
Field identification & locations
Identify by its waxy appearance and shell-like (conchoidal) fractures where it has been chipped. Commonly found in gravel pits, riverbeds, and sedimentary rock outcrops.
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