sedimentary
Chert / Chalcedony (likely carnelian or flint variety)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Translucent grey to reddish-brown. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Translucent grey to reddish-brown
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Translucent grey to reddish-brown. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the accumulation of silica-rich microfossils or precipitation from hydrothermal fluids in sedimentary rock cavities. This specimen shows a waxy, translucent interior attached to a rough, iron-stained host rock or cortex.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges. Currently used as an ornamental stone, for lapidary work (jewelry), and as a collector's specimen.
Geological facts
Because of its cryptocrystalline structure, it breaks into extremely sharp edges. It has been used since the Stone Age to create arrowheads, scrapers, and knives.
Field identification & locations
Identify by its 'conchoidal' (shell-like) fracture pattern and its ability to scratch glass. Often found as nodules within limestone or as river-worn pebbles. Common in regions with ancient seabed deposits.
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