sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
AI-generated identification · may be incorrectHardness: 7.0 (Mohs); Color: Brown, gray, and tan; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 7
- Color
- Brown, gray, and tan
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7.0 (Mohs); Color: Brown, gray, and tan; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Forms through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or via chemical precipitation from groundwater within limestone or chalk beds.
Uses & applications
Historically used for stone tools and strike-a-lights; currently used in construction aggregate and as a collector's specimen.
Geological facts
Chert has been used by humans for millions of years to create sharp-edged tools like arrowheads because of its predictable conchoidal fracturing.
Field identification & locations
Identify in the field by its waxy appearance, extreme hardness (it will scratch glass), and sharp, shell-like fracture edges. Commonly found in nodular form within carbonate rocks.
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