mineral
Quartz geode slice
Quartz (SiO₂), likely chalcedony-lined geode with drusy quartz
AI-generated identification · may be incorrectThe specimen has a dark, fine-grained host rock and a bright white, sparkly quartz/chalcedony rim. Quartz is Mohs 7, with vitreous to dull luster, trigonal crystal structure, and no cleavage; the apparent crystals are tiny drusy grains.
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Physical properties
The specimen has a dark, fine-grained host rock and a bright white, sparkly quartz/chalcedony rim. Quartz is Mohs 7, with vitreous to dull luster, trigonal crystal structure, and no cleavage; the apparent crystals are tiny drusy grains.
Formation & geological history
Likely formed when silica-rich groundwater filled cavities in volcanic rock, depositing chalcedony and later quartz crystals; the host may be basalt or another volcanic rock. Such geodes commonly formed in Cenozoic volcanic terrains, though the exact age cannot be determined visually.
Uses & applications
Used as a decorative, lapidary, and collecting specimen; attractive polished slices may be displayed or incorporated into jewelry. This example appears more suitable for educational or cabinet display than high-end jewelry.
Geological facts
The white granular border is consistent with drusy quartz, whose many microscopic crystal faces produce sparkle. The dark interior may be altered volcanic matrix rather than part of the geode cavity.
Field identification & locations
Identify by its very hard, glassy white crystalline lining that can scratch glass, lack of fizzing in dilute acid, and conchoidal fracture. Common sources include Brazil, Uruguay, Mexico, and the western United States.
