mineral
Banded Agate
Agate (Cryptocrystalline variety of Quartz, SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Dark brown to black with white/grey banding; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: 2.58-2.64
- Hardness
- 6
- Color
- Dark brown to black with white/grey banding
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Dark brown to black with white/grey banding; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: 2.58-2.64
Formation & geological history
Formed through the deposition of silica from groundwater into cavities (vesicles) within igneous volcanic rocks such as basalt. The banding represents different pulses of mineral-rich fluids over thousands of years.
Uses & applications
Used primarily in lapidary arts for jewelry, decorative carvings, and as a collector's specimen. Historically used for making precision burnishing tools and mortar and pestles due to its hardness.
Geological facts
Agate is named after the Achates River in Sicily where it was first discovered. No two agates are exactly alike, making each specimen unique. The banding can sometimes contain thousands of individual layers.
Field identification & locations
Identify by its characteristic concentric or irregular banding, waxy luster when tumbled, and its inability to be scratched by a steel knife. Commonly found in riverbeds, beaches, and volcanic regions worldwide.
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