mineral
Banded Agate (Onyx type)
Silicon dioxide (SiO2)
Hardness: 6.5-7 Mohs; Color: Black with white bands; Luster: Vitreous to waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.6
- Hardness
- 6
- Color
- Black with white bands
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5-7 Mohs; Color: Black with white bands; Luster: Vitreous to waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.6
Formation & geological history
Formed in cavities of volcanic rocks or ancient lavas, where silica-rich groundwater deposited layers of chalcedony over vast geological timescales.
Uses & applications
Used primarily in jewelry, cabochons, decorative carvings, and as a healing stone in metaphysical practices. Also historically used for making cameos.
Geological facts
The parallel white and black bands are characteristic of Onyx, a sub-type of chalcedony. It has been used since antiquity for ornaments and was highly prized by Romans.
Field identification & locations
Identify by its distinct, often parallel banding and waxy surface when polished. Commonly found in Brazil, India, and Madagascar.
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Mineral/Rock
Banded Gneiss (River Rock/Pebble)
Gneiss (specifically a banded variety often found as a river rock)
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Biotite Schist
Biotite-rich Schist [K(Mg,Fe)3AlSi3O10(F,OH)2]
metamorphic