mineral
Chalcedony (River Pebble)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 Mohs; Color: Translucent white to light grey; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None; Fracture: Conchoidal
- Hardness
- 6
- Color
- Translucent white to light grey
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 Mohs; Color: Translucent white to light grey; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None; Fracture: Conchoidal
Formation & geological history
Formed from the deposition of silica-rich water in cavities or fissures within volcanic or sedimentary rocks, then weathered out and smoothed by water transport in a river or stream environment.
Uses & applications
Used for lapidary work, jewelry (beads and cabochons), tumbled stones for collectors, and historical use for tool making due to its fracture pattern.
Geological facts
Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen without a microscope. It is the same family as agate and jasper, but typically lacks the distinct banding or opacity of those varieties.
Field identification & locations
Identify by its waxy luster, smooth water-worn surface, and ability to scratch glass. Commonly found in riverbeds, gravel pits, and coastal areas.
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Arenite (SiO2 based)
sedimentary
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metamorphic
Gypsum (variety Selenite or Alabaster)
Calcium sulfate dihydrate (CaSO4·2H2O)
Mineral
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Granite
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igneous