sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Grey, brown, yellowish, and black; Luster: Waxy to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Grey, brown, yellowish, and black
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grey, brown, yellowish, and black; Luster: Waxy to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed in marine environments through the accumulation of silica-rich organic remains or chemical precipitation within limestone or chalk beds. Most specimens can range from hundreds of millions to billions of years old.
Uses & applications
Historically used for stone tools and starting fires; currently used for lapidary work, jewelry, and archaeological study.
Geological facts
Chert has been used by humans for hundreds of thousands of years to create sharp-edged tools like arrowheads and knives due to its predictable conchoidal fracturing.
Field identification & locations
Identify in the field by its waxy texture, extreme hardness (scratches glass), and shell-like (conchoidal) fracture patterns. Often found as nodules within limestone or along riverbeds.
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