mineral

Quartz geode

Microcrystalline quartz (chalcedony) with drusy quartz crystals; SiO₂

AI-generated identification · may be incorrect

Typically Mohs hardness 7, vitreous to dull luster, white/cream or rust-stained outer rind, and a hollow cavity lined with sparkling quartz crystals. Quartz is trigonal and has no cleavage; the brown color is likely iron-oxide staining, with possible minor calcite or feldspar in the matrix.

Identified August 17, 2026More mineral →

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Physical properties

Formation & geological history

Formed when silica-rich groundwater filled a gas vesicle or cavity in volcanic rock, depositing chalcedony and later quartz crystals inward from the walls. The specimen’s exact age cannot be determined visually; geodes commonly form during cooling and alteration of volcanic rocks over millions of years.

Uses & applications

Used as a decorative and lapidary specimen, including polished halves, bookends, and jewelry components; attractive drusy examples are popular with collectors.

Geological facts

The cavity and inward-pointing crystals are diagnostic of a geode rather than a solid quartz nodule. Crystal sparkle depends on crystal size, light, and the degree of iron staining.

Field identification & locations

Look for a rounded, resistant outer rind and a hollow interior lined with crystals; quartz will scratch glass but not be scratched by a steel knife. Common sources include Brazil, Uruguay, Mexico, Morocco, and the western United States.