mineral
Chalcedony (Common Opal or Agate variant)
Silicon dioxide (SiO2) with trace hydration
Hardness: 6.5-7 (Mohs); Color: Pale yellow, translucent to waxy; Luster: Vitreous to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); SG: 2.6
- Hardness
- 6
- Color
- Pale yellow, translucent to waxy
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Pale yellow, translucent to waxy; Luster: Vitreous to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); SG: 2.6
Formation & geological history
Formed via low-temperature deposition of silica-rich groundwater in cavities of volcanic or sedimentary rocks. This specimen appears to be a weathered river or field pebble.
Uses & applications
Used for lapidary work, jewelry (cabochons), and as a collector's specimen. Known as a 'healing stone' in metaphysical circles.
Geological facts
Chalcedony is made of microcrystalline quartz and moganite. When it shows banding it is called agate; when it is translucent and waxy like this, it is often just called chalcedony or common opal.
Field identification & locations
Identify by its waxy luster, conchoidal (shell-like) fracture, and inability to be scratched by a steel knife. Best found in gravel beds or volcanic regions after rain.
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