sedimentary
Agate Pebble
Silicon dioxide (SiO2) - Chalcedony variety
Hardness: 6.5-7 on Mohs scale; Color: Brown, grey, with orange/yellow iron oxide patches; Luster: Waxy to vitreous; Crystal structure: Microcrystalline (cryptocrystalline) quartz; Cleavage: None, exhibits conchoidal fracture; Specific gravity: 2.6-2.7
- Hardness
- 6
- Color
- Brown, grey, with orange/yellow iron oxide patches
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Brown, grey, with orange/yellow iron oxide patches; Luster: Waxy to vitreous; Crystal structure: Microcrystalline (cryptocrystalline) quartz; Cleavage: None, exhibits conchoidal fracture; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the deposition of silica-rich groundwater solutions in cavities of ancient rocks, typically volcanic or sedimentary, over millions of years
Uses & applications
Used for making jewelry, ornamental carvings, polished display specimens, and in lapidary arts
Geological facts
Agate is a form of chalcedony that often forms in concentric bands. The orange coloration on this specimen is typically due to iron oxide staining (rust) that penetrated the porous outer layers or fractures.
Field identification & locations
Found worldwide in riverbeds, beaches, and glacial till where weathering has released them from host rocks. Identify by its waxy luster, smooth water-worn surface, and microcrystalline structure.
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