sedimentary
Micro-crystalline Quartz Pebble (Chert)
Silicon dioxide (SiO2)
Hardness: 7 Mohs; Color: Tan to light brown; Luster: Dull or waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 Mohs
- Color
- Tan to light brown
- Luster
- Dull or waxy
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Physical properties
Hardness: 7 Mohs; Color: Tan to light brown; Luster: Dull or waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed via the accumulation of silica-rich organic remains or chemical precipitation in oceanic or lacustrine environments. Often found as nodules in limestone or as recycled river gravels.
Uses & applications
Historically used for stone tools; currently used as construction aggregate, landscaping gravel, and for lapidary tumbling.
Geological facts
Chert is so hard it can create sparks when struck against steel. It is one of the most common materials used by prehistoric humans for creating arrowheads and scrapers.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a steel blade) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds and gravel pits.
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