sedimentary
Chert (Nodule)
Chert (Silicon Dioxide, SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, and olive green patches; Luster: Dull to waxy; Crystal structure: Microcrystalline (Cryptocrystalline); Cleavage: None (has conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, and olive green patches
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, and olive green patches; Luster: Dull to waxy; Crystal structure: Microcrystalline (Cryptocrystalline); Cleavage: None (has 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 within limestone or chalk beds. This specimen appears water-worn, potentially from a riverbed environment.
Uses & applications
Historically used for making stone tools and arrowheads; currently used as road aggregate, in landscaping, and occasionally for flint-knapping enthusiasts.
Geological facts
Chert is extremely durable and chemically stable. When it is high-purity and brightly colored, it is often called Jasper; when it is translucent, it is known as Chalcedony.
Field identification & locations
Identify in the field by its extreme hardness (will scratch steel and glass) and its smooth, shell-like (conchoidal) fracture pattern. It often has a thin, chalky outer weathering rind.
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