sedimentary
Chert (Nodule)
Chert (Cryptocrystalline Silica, SiO2)
Hardness: 6.5-7 Mohs. Color: Off-white, tan, and gray with iron staining. Luster: Waxy to dull. Structure: Microcrystalline. Specific Gravity: 2.6-2.7. Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Off-white, tan, and gray with iron staining
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs. Color: Off-white, tan, and gray with iron staining. Luster: Waxy to dull. Structure: Microcrystalline. Specific Gravity: 2.6-2.7. Cleavage: None (conchoidal fracture).
Formation & geological history
Formed via the accumulation of silica-rich organic remains or chemical precipitation within limestone or chalk beds, often during the Paleozoic or Mesozoic eras.
Uses & applications
Historically used for stone tools (arrowheads). Modernly used in construction aggregate, road base, and as decorative landscaping stones.
Geological facts
Chert is extremely durable and chemically resistant. Flint is a high-quality variety of chert. It was one of the most important materials for early human technological development due to its sharp edges.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel nail) and characteristic curved 'glass-like' fractures. Commonly found in riverbeds or weathered out of carbonate rock outcrops.
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