mineral
Agate Geode
Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Gray, blue, white, tan; Luster: Vitreous to waxy; Structure: Microcrystalline (Trigonal); Cleavage: None/Conchoidal fracture.
- Hardness
- 6
- Color
- Gray, blue, white, tan
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5-7 Mohs; Color: Gray, blue, white, tan; Luster: Vitreous to waxy; Structure: Microcrystalline (Trigonal); Cleavage: None/Conchoidal fracture.
Formation & geological history
Formed by the deposition of silica-rich groundwater within vesicles (gas bubbles) in volcanic rocks or cavities in sedimentary rocks over millions of years.
Uses & applications
Used for lapidary arts, jewelry, high-end home decor, bookends, and collecting. Historically used for balance and energy in folk traditions.
Geological facts
The banding in agates is caused by periodic changes in the composition of the fluids entering the cavity; this specific specimen shows a 'waterline' or horizontal banding characteristic of gravity settling.
Field identification & locations
Look for rounded, potato-like nodules with a rough, weathered exterior and a high density compared to common river stones. Found globally in Brazil, Uruguay, and the US.
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Mineral/Rock