sedimentary
Geode
Quartz / Chalcedony nodule
Hardness of 7 on the Mohs scale, colors vary from white, gray, brown to clear quartz crystal interiors, vitreous to dull luster, cryptocrystalline to microcrystalline structure with macro-quartz crystals lining the inner cavity.
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Physical properties
Hardness of 7 on the Mohs scale, colors vary from white, gray, brown to clear quartz crystal interiors, vitreous to dull luster, cryptocrystalline to microcrystalline structure with macro-quartz crystals lining the inner cavity.
Formation & geological history
Formed in sedimentary rock formations (like limestone or shale) or volcanic ash beds where mineral-rich groundwater deposits silica inside hollow cavities or nodules over millions of years.
Uses & applications
Popular as mineral specimens, in decorative displays, crystal healing, and jewelry making.
Geological facts
Geodes form outward from the cavity walls, meaning the outer shell is usually tougher chalcedony while the inner crystals are often sparkling quartz or sometimes amethyst.
Field identification & locations
Found in regions with significant limestone or volcanic deposits worldwide, often identified by their roundish, nodular external shape which feels heavy for its size.
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