Sedimentary
Chert
Silicon dioxide (SiO2) - Microcrystalline quartz
Hardness: 6.5-7 on Mohs scale. Color: Highly variable, often brown, gray, black, or red. Luster: Waxy to dull. Crystal structure: Microcrystalline. Cleavage: None, exhibits conchoidal fracture. Specific gravity: ~2.6.
- Hardness
- 6
- Color
- Highly variable, often brown, gray, black, or red
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Highly variable, often brown, gray, black, or red. Luster: Waxy to dull. Crystal structure: Microcrystalline. Cleavage: None, exhibits conchoidal fracture. Specific gravity: ~2.6.
Formation & geological history
Formed as a chemical sedimentary rock, typically from the precipitation of silica from groundwater or the accumulation of siliceous marine micro-organisms like diatoms and radiolarians.
Uses & applications
Historically used for making stone tools (like arrowheads) due to its conchoidal fracture. Sometimes used as a low-grade aggregate in construction.
Geological facts
Flint is a specific type of chert found in chalk or marly limestone. Because of its hardness and ability to produce sparks when struck against steel, it was essential for early fire-starting and flintlock firearms.
Field identification & locations
Identify by its waxy luster, hardness (scratches glass), and distinct conchoidal (shell-like) fracture. Commonly found in sedimentary basins worldwide, often as nodules in limestone.
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