sedimentary
Chert (Common Opal/Chalcedony nodule)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Tan, beige, creamy white; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Tan, beige, creamy white
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Tan, beige, creamy white; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed primarily through the chemical precipitation of silica-rich fluids within sedimentary host rocks like limestone or chalk, often as nodules or replacement layers.
Uses & applications
Historically used for stone tools (arrowheads); currently used in decorative landscaping, as a source of abrasive material, and for lapidary tumbling.
Geological facts
Chert has been used by humans for millions of years because its conchoidal fracture creates razor-sharp edges. It is often found in prehistoric archaeological sites.
Field identification & locations
Identify in the field by its waxy appearance, extreme hardness (scratches glass), and shell-like (conchoidal) fracture pattern. Commonly found in riverbeds or limestone outcrops.
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