sedimentary
Chert (varietal: Jasper or Flint)
Silicon Dioxide (SiO2) - Cryptocrystalline Quartz
Hardness: 7 on Mohs scale; Color: Tan, brown, or grayish with dark inclusions; Luster: Dull to waxy; Crystal Structure: Cryptocrystalline (microscopic crystals); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, or grayish with dark inclusions
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, or grayish with dark inclusions; Luster: Dull to waxy; Crystal Structure: Cryptocrystalline (microscopic crystals); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in groundwater. These specimens can range from hundreds of millions to billions of years old, often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools and weapons due to sharp edges; currently used for road surfacing, jewelry (tumbled stones), and as a decorative landscaping rock.
Geological facts
Chert was one of the most vital materials for early humans because its conchoidal fracture allows it to be 'knapped' into razor-sharp arrowheads and scrapers. Depending on impurities, it is known as Jasper (red/brown), Flint (dark gray/black), or Agate (banded).
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its curved, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds, glacial tills, and sedimentary rock outcrops.
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