sedimentary
Chert (specifically Jaspery Chert)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Reddish-brown to tan; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Reddish-brown to tan
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Reddish-brown to tan; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed primarily through the chemical precipitation of silica or the accumulation of silica-rich organic debris (like radiolarians) on the ocean floor, followed by diagenesis.
Uses & applications
Historically used for stone tools (arrowheads) due to conchoidal fracturing; used today as decorative stones, in landscaping, and as lapidary material.
Geological facts
Chert is so hard it can strike sparks from steel, which led to its historical use as flint. This specimen shows the characteristic waxy luster and sharp, jagged edges typical of microcrystalline silica.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a steel knife), its smooth shell-like (conchoidal) fracture, and its lack of visible grains. Common in limestone and chalk formations.
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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