mineral

Quartz geode (likely chalcedony-lined)

Quartz, SiO₂; microcrystalline chalcedony with drusy quartz

AI-generated identification · may be incorrect

Typically Mohs hardness 7, vitreous to waxy luster, white to gray or tan coloration, and hexagonal quartz crystals; massive chalcedony lacks visible cleavage, while quartz has indistinct cleavage. The cavity is lined with sparkling drusy crystals.

Identified August 14, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills gas cavities or dissolution voids in volcanic rock, depositing chalcedony and later quartz crystals. Individual geodes may range from Cenozoic to much older, depending on the host formation.

Uses & applications

Used as a decorative and display specimen; attractive varieties may be cut into cabochons or slabs. Common geodes are also sold for education, collecting, and interior décor.

Geological facts

The outer banded shell commonly records repeated silica deposition, while the open cavity formed before crystal growth. Gray-brown coloration may result from iron or other trace impurities.

Field identification & locations

Identify by a hollow or partly hollow chalcedony shell, concentric banding, waxy surfaces, and sparkling quartz lining; acid resistance and hardness help distinguish it from calcite geodes. Common sources include Brazil, Uruguay, Mexico, and the United States.