sedimentary
Blue Agate (Dyed Chalcedony)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: Vivid blue (unnatural saturation), Luster: Vitreous to waxy, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None, Specific Gravity: 2.60-2.65
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: Vivid blue (unnatural saturation), Luster: Vitreous to waxy, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None, Specific Gravity: 2.60-2.65
Formation & geological history
Formed as a microcrystalline variety of silica, typically occurring within volcanic rock cavities or sedimentary geodes. Natural blue agate is rare and pale; this specific intense blue is achieved through dyeing translucent chalcedony.
Uses & applications
Commonly used for decorative ornaments, tumbled stones for collectors, 'worry stones', inexpensive costume jewelry, and lapidary practice.
Geological facts
Agate has been used for over 3,000 years, originally named after the Achates River in Sicily. Most bright blue agate found in gift shops is actually Brazilian chalcedony that has been soaked in a chemical solution to achieve the electric blue hue.
Field identification & locations
Identify in the field by its conchoidal fracture and hardness (won't be scratched by a steel blade). To identify if it is dyed, look for color concentration in small cracks or bands that look too vibrant to be natural. Commonly found in Brazil, Uruguay, and India.
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