mineral

Agate Geode

Silicon Dioxide (SiO2) - Banded Chalcedony with Quartz

AI-generated identification · may be incorrect

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)

Identified July 25, 2026More mineral →

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Physical properties

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).