mineral
Banded Agate
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 6.5 - 7 on the Mohs scale. Color: Grayish-blue, charcoal, and translucent white banding. Luster: Vitreous to waxy after polishing. Crystal System: Trigonal (microcrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.58 - 2.64.
- Hardness
- 6
- Color
- Grayish-blue, charcoal, and translucent white banding
- Luster
- Vitreous to waxy after polishing
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Physical properties
Hardness: 6.5 - 7 on the Mohs scale. Color: Grayish-blue, charcoal, and translucent white banding. Luster: Vitreous to waxy after polishing. Crystal System: Trigonal (microcrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.58 - 2.64.
Formation & geological history
Forms primarily as secondary deposits in cavities within volcanic or metamorphic rocks (such as basalt or void spaces in lava). Silica-rich solutions precipitate slowly layer-by-layer over time, forming chalcedony and quartz banding.
Uses & applications
Widely used for lapidary arts, jewelry making, polished tumbled stones, carved decorative objects, and crystal healing collections. Historically used for intaglios and cameo carvings.
Geological facts
The distinct bands in agate are formed when silica fluid periodically floods rock cavities, depositing microscopic crystals of quartz. Agate gets its name from the Dirillo (formerly Achates) River in Sicily where it was discovered in ancient times.
Field identification & locations
Identified by its distinctive concentric or parallel color banding, smooth texture, and waxy glass-like appearance when polished. Common worldwide, especially in Brazil, Uruguay, Madagascar, India, and the United States.
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