sedimentary
Geode
Quartz / Chalcedony nodule with mineralized cavity
Hardness: 7 (quartz), Color: Varies with exterior being grey/brown limestone and interior showing white, clear, or amber quartz crystals, Luster: Vitreous to dull, Crystal structure: Trigonal (quartz), Specific gravity: 2.65
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Physical properties
Hardness: 7 (quartz), Color: Varies with exterior being grey/brown limestone and interior showing white, clear, or amber quartz crystals, Luster: Vitreous to dull, Crystal structure: Trigonal (quartz), Specific gravity: 2.65
Formation & geological history
Formed in sedimentary environments, typically within limestone or shale cavities, through the groundwater precipitation of silica-rich solutions over millions of years.
Uses & applications
Popular in mineral collecting, lapidary art, jewelry making, and metaphysical practices.
Geological facts
Geodes start as hollow bubbles in rock, often from animal burrows, roots, or nodules, which slowly fill in with mineral layers from the outside in.
Field identification & locations
Commonly identified by their rounded, potato-like exterior and a hollow or crystal-lined center when cracked open. Found worldwide, notably in Mexico, Brazil, and the US (e.g., Indiana, Kentucky, Utah).
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