sedimentary
Geode
Quartz nodule / Chalcedony-lined cavity
Hardness of 7 on the Mohs scale for the quartz interior. Exterior is typically bumpy, weathered limestone or volcanic rock. Luster is vitreous to dull. Crystal structure is trigonal for internal quartz crystals.
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Physical properties
Hardness of 7 on the Mohs scale for the quartz interior. Exterior is typically bumpy, weathered limestone or volcanic rock. Luster is vitreous to dull. Crystal structure is trigonal for internal quartz crystals.
Formation & geological history
Formed in hollow areas in sedimentary or igneous rocks, where mineral-rich groundwater seeps in and slowly deposits microcrystalline silica (chalcedony) and quartz crystals over millions of years.
Uses & applications
Popular in lapidary arts, specimen collecting, decorative home display, and metaphysical practices.
Geological facts
Geodes look entirely ordinary and rough on the outside, which makes cracking them open a popular and exciting activity for rockhounds and geologists alike.
Field identification & locations
Found worldwide in limestone formations, volcanic ash beds, and deserts. Look for rounded, nodular rocks that feel unusually lightweight for their size or rattle when shaken.
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