sedimentary
Banded Agate (Onyx variant)
Silicon dioxide (SiO2)
Hardness: 6.5-7 Mohs; Color: Honey-yellow with dark brown/black parallel bands; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Honey-yellow with dark brown/black parallel bands
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 Mohs; Color: Honey-yellow with dark brown/black parallel bands; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed from the deposition of silica from groundwater in the cavities of igneous or sedimentary rocks, often resulting in rhythmic crystallization layers. Ages vary from recently formed to millions of years old.
Uses & applications
Primarily used in jewelry for cabochons, lapidary carvings, decorative beads, and as an ornamental collector specimen.
Geological facts
The parallel nature of the bands technically classifies this as an Onyx variant of Chalcedony. In ancient times, it was believed to provide physical strength and protection to the wearer.
Field identification & locations
Identify in the field by its distinct parallel banding, translucency when held to light, and waxy luster. Common in volcanic regions of Brazil, Uruguay, and India.
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