sedimentary
Chert (Commonly known as Flint or Jasper)
Chert (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: Brownish-red to tan, Luster: Waxy to dull, Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.5-2.8
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: Brownish-red to tan, Luster: Waxy to dull, Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.5-2.8
Formation & geological history
Formed by the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within sedimentary beds. These specimens can range from hundreds of millions to several billions of years old.
Uses & applications
Historically used for making stone tools (arrowheads). Currently used as decorative stone, in construction aggregate, and occasionally for lapidary work (tumbling).
Geological facts
Chert is so hard it can create sparks when struck against steel, a property that led to its use in fire-starting and early firearms (flintlocks).
Field identification & locations
Identified by its waxy appearance, extreme hardness (it will scratch glass), and smooth, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds and limestone outcrops.
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