sedimentary
Chert (varieties include Flint and Jasper)
Silicon Dioxide (SiO2) / Microcrystalline Quartz
Hardness: 7 (Mohs scale), Color: Cream, grey, tan, and brown with waxy luster. Crystal structure: Cryptocrystalline. Cleavage: None (has conchoidal fracture). Specific Gravity: 2.5 - 2.8.
- Color
- Cream, grey, tan, and brown with waxy luster
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Physical properties
Hardness: 7 (Mohs scale), Color: Cream, grey, tan, and brown with waxy luster. Crystal structure: Cryptocrystalline. Cleavage: None (has conchoidal fracture). Specific Gravity: 2.5 - 2.8.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by the chemical precipitation of silica in groundwater. Often found as nodules within limestone or chalk beds.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) and fire-starting. Currently used as road surfacing, in construction aggregate, and as a low-cost gemstone for lapidary work.
Geological facts
Chert has been used by humans for over 2 million years to create tools. It breaks with extremely sharp edges, often sharper than a surgical steel scalpel. Varieties like Flint were essential for early firearms (flintlocks).
Field identification & locations
Identify in the field by its waxy luster, hardness (it will scratch glass), and its distinct conchoidal (shell-like) fracture patterns. It is common in riverbeds and limestone outcrops globally.
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