mineral
Banded Agate (Onyx type)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs); Color: Black with white/grey bands; Luster: Vitreous to waxy; Crystal structure: Trigonal (cryptocrystalline); Specific gravity: 2.58-2.64
- Hardness
- 6
- Color
- Black with white/grey bands
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Black with white/grey bands; Luster: Vitreous to waxy; Crystal structure: Trigonal (cryptocrystalline); Specific gravity: 2.58-2.64
Formation & geological history
Formed in cavities of volcanic rock (basalt) or ancient lava flows as silica-rich water percolates through voids, depositing layers of microcrystalline quartz over thousands of years.
Uses & applications
Widely used in jewelry (rings, pendants), carvings, decorative ornaments, and as tumbled stones for metaphysical collecting.
Geological facts
The distinct banding is caused by rhythmic crystallization pulses. When the bands are parallel and black/white, it is specifically referred to as Onyx.
Field identification & locations
Identify by its waxy luster and the presence of fine, concentric or parallel banding. It is often found in riverbeds or coastal areas where volcanic rocks have weathered away. Common in Brazil, India, and the Lake Superior region of the US.
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Arenite (SiO2 based)
sedimentary
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Schist
Metamorphic
Epidote
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metamorphic
Gypsum (variety Selenite or Alabaster)
Calcium sulfate dihydrate (CaSO4·2H2O)
Mineral
Nephrite Jade
Nephrite
Mineral/Rock
Banded Gneiss (River Rock/Pebble)
Gneiss (specifically a banded variety often found as a river rock)
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