mineral
Quartz Geode with Chalcedony
Silicon Dioxide (SiO2)
Mohs hardness of 7. Luster ranges from vitreous to waxy. Color varies from clear and tan/yellow iron-stained quartz crystals to translucent grayish-blue chalcedony core. Trigonal crystal system.
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Physical properties
Mohs hardness of 7. Luster ranges from vitreous to waxy. Color varies from clear and tan/yellow iron-stained quartz crystals to translucent grayish-blue chalcedony core. Trigonal crystal system.
Formation & geological history
Formed in cavities within volcanic or sedimentary rocks where silica-rich fluids precipitated over long periods, often deposited in layers of microcrystalline chalcedony and macrocrystalline quartz.
Uses & applications
Popular for mineral specimen collecting, lapidary work, decorative display pieces, and metaphysical uses.
Geological facts
Geodes are hollow, spherical rocks lined with crystals, but when fully filled in, they are referred to as nodules or thundereggs. Iron oxide staining often gives quartz crystals a warm golden-brown tint.
Field identification & locations
Look for a rough exterior shell with a sparkling crystalline interior or banding. Widely found in basaltic lava beds and limestone formations in Brazil, Uruguay, Madagascar, and parts of the Midwestern USA.
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