mineral

Quartz geode / chalcedony nodule

Silica, primarily quartz (SiO₂), with microcrystalline chalcedony

AI-generated identification · may be incorrect

Gray-brown botryoidal outer chalcedony encloses a cavity lined with translucent drusy quartz crystals. Quartz hardness is Mohs 7, vitreous luster, hexagonal crystal structure, no cleavage, and specific gravity about 2.65.

Identified August 8, 2026More mineral →

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Physical properties

Formation & geological history

Likely formed when silica-rich groundwater filled gas vesicles or cavities in volcanic rock, depositing chalcedony and later quartz crystals. Such geodes commonly formed in Cenozoic basaltic volcanic environments, though the exact age and locality cannot be determined from the image.

Uses & applications

Used as a decorative and collectible specimen; larger polished geodes are popular in interiors and lapidary work. Quartz also has extensive industrial uses in glass, electronics, abrasives, and engineered stone.

Geological facts

The dark exterior may be iron- or manganese-stained chalcedony, while the sparkling interior consists of tiny quartz crystals. The specimen appears naturally broken rather than professionally cut.

Field identification & locations

Identify by its hollow or partially hollow silica rind, waxy chalcedony surface, and glassy crystal sparkle; quartz should scratch ordinary glass. Common sources include Brazil, Uruguay, Mexico, Morocco, and the western United States.