mineral
Chalcedony (Blue Agate Nodules)
Silicon Dioxide (SiO2)
Hardness: 6.5-7.0 (Mohs); Color: Pale blue to translucent white with yellow-orange oxidation; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: None; Specific Gravity: 2.58-2.64.
- Hardness
- 6
- Color
- Pale blue to translucent white with yellow-orange oxidation
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7.0 (Mohs); Color: Pale blue to translucent white with yellow-orange oxidation; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: None; Specific Gravity: 2.58-2.64.
Formation & geological history
Formed through the deposition of silica from groundwater in the cavities of volcanic rocks (basalts and rhyolites) or sedimentary rocks. These nodules are often rounded due to alluvial transport and weathering over millions of years.
Uses & applications
Used primarily in lapidary arts, jewelry (cabochons and beads), ornamental carvings, and by mineral collectors. It is also historically used for making precision bearings and mortars/pestles due to its hardness.
Geological facts
The blue tint in chalcedony is often caused by the Tyndall effect, which is the scattering of light by fine particles, similar to why the sky looks blue. If the stone has banding, it is technically classified as Agate.
Field identification & locations
Identify in the field by its waxy luster, conchoidal fracture, and translucency when held to light. Common in arid alluvial plains or volcanic regions like the American Southwest, Brazil, and Namibia.
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