mineral
Quartz geode
Microcrystalline and crystalline quartz, SiO₂, likely with chalcedony and iron-oxide staining
AI-generated identification · may be incorrectTypically Mohs hardness 7, vitreous to drusy luster, white to gray crystals, and no cleavage; the brown outer rind is likely weathered volcanic or sedimentary host rock. The hollow cavity is lined with small quartz crystals, possibly mixed with calcite or other secondary minerals.
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Physical properties
Typically Mohs hardness 7, vitreous to drusy luster, white to gray crystals, and no cleavage; the brown outer rind is likely weathered volcanic or sedimentary host rock. The hollow cavity is lined with small quartz crystals, possibly mixed with calcite or other secondary minerals.
Formation & geological history
Formed when mineral-rich groundwater filled a cavity in volcanic rock or sediment, depositing chalcedony and later quartz crystals over long periods, commonly during the Cenozoic or older. The precise age and host rock cannot be determined from the photograph.
Uses & applications
Used as a decorative specimen, lapidary material, and collector display piece; attractive crystal-lined geodes may be sold as home décor or jewelry components.
Geological facts
The specimen’s hollow interior and sparkling drusy coating are characteristic of a geode, while the cream-brown rind reflects alteration and iron staining.
Field identification & locations
Identify by the rounded hollow shell and inward-pointing quartz crystals; quartz is commonly found in volcanic terrains and sedimentary cavities worldwide, including Brazil, Uruguay, Mexico, and the United States. A hardness test, acid test, and close inspection are needed to distinguish quartz from calcite.
