mineral

Polished quartz geode slice

Quartz (SiO₂), likely chalcedony-lined geode with drusy quartz crystals

AI-generated identification · may be incorrect

Hardness 7 (quartz); gray-white, translucent to opaque, with a dark hollow center and sparkling crystalline rim. Vitreous to waxy luster; quartz is trigonal and lacks cleavage, with conchoidal fracture. The dark area may be iron/manganese staining or inclusions, not necessarily amethyst.

Identified August 21, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills gas vesicles or cavities in volcanic rock, depositing chalcedony and later quartz crystals. The specimen’s exact geological age and locality cannot be determined from the image; geodes commonly form in Cenozoic to Paleozoic volcanic or sedimentary settings.

Uses & applications

Used as a decorative display stone, cabochon, paperweight, or jewelry component; not generally used structurally.

Geological facts

The exterior was cut and polished, revealing an internal cavity lined with microcrystalline quartz. A strong glassy sparkle and lack of obvious banding distinguish it from many agates.

Field identification & locations

Identify by its rounded nodule shape, quartz hardness, crystalline cavity, and conchoidal fracture; common sources include Brazil, Uruguay, Mexico, Morocco, and the United States. Exact identification would benefit from locality, hardness, and acid/magnet tests.