sedimentary
Chert (Flint)
Microcrystalline Silicon Dioxide (SiO2)
Hardness: 6.5-7 Mohs; Color: Brown, tan, or grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.58-2.91
- Hardness
- 6
- Color
- Brown, tan, or grey
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Brown, tan, or grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.58-2.91
Formation & geological history
Formed in marine environments through the accumulation of silica-rich organic remains or chemical precipitation within limestone/chalk beds. It can date from almost any geological era.
Uses & applications
Historically used for stone tools and weapons (arrowheads); currently used in road construction, as grinding media, and as a low-cost gemstone for jewelry.
Geological facts
Chert has been used by humans for millions of years due to its ability to break into sharp edges. It is also known as flint when it occurs in chalk or marly limestone.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel), waxy appearance, and characteristic shell-like (conchoidal) fracture edges. Commonly found in riverbeds or as nodules in limestone.
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