sedimentary
Chert (Flint)
Chert (Microcrystalline or cryptocrystalline Quartz, SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, white, with brown inclusions; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, white, with brown inclusions
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, white, with brown inclusions; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds. Most notable deposits range from the Precambrian to recent times.
Uses & applications
Historically used for stone tools and starting fires; currently used as a road aggregate, in jewelry as tumbled stones, and as a decorative landscaping stone.
Geological facts
Flint is a variety of chert that has been used by humans for over two million years to create sharp-edged tools and weapons. It produces sparks when struck against steel due to the hardness of the silica.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife), conchoidal fracture (curved, glass-like breaks), and smooth, waxy texture. Commonly found in riverbeds and within sedimentary rock outcrops.
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