sedimentary
Agate
Silicon dioxide (SiO2) - variety of chalcedony
Hardness: 6.5-7 Mohs; Color: Brown, tan, white, translucent; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None; Fracture: Conchoidal; Specific gravity: 2.58-2.64
- Hardness
- 6
- Color
- Brown, tan, white, translucent
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 Mohs; Color: Brown, tan, white, translucent; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None; Fracture: Conchoidal; Specific gravity: 2.58-2.64
Formation & geological history
Formed as a secondary mineral in cavities (vesicles) of volcanic rocks or sedimentary environments through the deposition of silica from groundwater. This specimen shows water-worn rounding, suggesting it was found in a river or coastal environment.
Uses & applications
Used for jewelry (cabochons), lapidary art, mortar and pestles, burnishing tools, and as a popular collector's item due to its unique banding patterns.
Geological facts
Agate is named after the Achates River in Sicily where it was first discovered. Every agate is unique, and its bands are formed by the pulse-like deposition of mineral-rich water over thousands of years.
Field identification & locations
Look for a waxy texture and translucency when held to Light. It often shows faint banding or 'eyes'. This specific piece is a river-tumbled nodule common in areas with ancient volcanic activity.
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