mineral
Agate Geode
Silicon Dioxide (SiO2) - Banded Chalcedony with Quartz
Hardness: 6.5 - 7 on Mohs scale. Color: Brown, tan, white, translucent clear quartz crystals. Luster: Waxy to vitreous (glassy). Structure: Microcrystalline (chalcedony) with trigonal quartz crystals in the hollow center. Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Brown, tan, white, translucent clear quartz crystals
- Luster
- Waxy to vitreous (glassy)
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Physical properties
Hardness: 6.5 - 7 on Mohs scale. Color: Brown, tan, white, translucent clear quartz crystals. Luster: Waxy to vitreous (glassy). Structure: Microcrystalline (chalcedony) with trigonal quartz crystals in the hollow center. Cleavage: None (conchoidal fracture).
Formation & geological history
Formed when silica-rich hydrothermal fluids filled gas cavities (vesicles) in igneous basaltic lava flows. Layers of microcrystalline chalcedony deposited sequentially along cavity walls, followed by macroscopic quartz crystal growth in the remaining hollow center.
Uses & applications
Popular among lapidaries, rock collectors, and home decor items. Small geode slices like this are often used for pendants, cabochons, and mineral display specimens.
Geological facts
Agates are defined by their concentric or fortification banding patterns. Geodes are unique because they remain hollow in the interior, allowing sparkling crystal druzy to form.
Field identification & locations
Identified by concentric chalcedony banding surrounding a hollow cavity lined with sparkling quartz druzy crystals. Commonly found in volcanic rock formations in Brazil, Uruguay, Mexico, and the USA (e.g., Oregon, Iowa).
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