mineral

Quartz geode

Silica geode; predominantly microcrystalline and crystalline quartz (SiO₂), possibly with chalcedony and minor calcite

AI-generated identification · may be incorrect

Hardness about 7 Mohs for quartz; gray-brown rough outer rind with a hollow cavity lined by pale gray/white drusy quartz crystals. Vitreous to dull luster, hexagonal quartz structure, no prominent cleavage, and specific gravity near 2.65.

Identified August 26, 2026More mineral →

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Physical properties

Formation & geological history

Likely formed when silica-rich groundwater filled a gas bubble or cavity in volcanic rock, depositing chalcedony and quartz inward from the walls. Geode formation commonly occurred during volcanic activity in the Mesozoic or Cenozoic, depending on locality.

Uses & applications

Used as a decorative specimen, lapidary material, and in crystal collecting; attractive crystal-lined pieces may be displayed or cut into halves. This appears more suitable for display than industrial use.

Geological facts

The cavity formed before the crystals grew, so crystal layers generally point inward toward the former void. The dark exterior may be weathered volcanic matrix or iron/manganese staining rather than the crystal material itself.

Field identification & locations

Identify by a hollow or partly hollow rounded nodule with inward-pointing quartz crystals and a dense outer rind; common sources include Brazil, Uruguay, Mexico, and the United States. Estimated value: roughly $15–$100, or $100–$300+ for unusually large, well-crystallized specimens.