sedimentary
Geode (Chert/Quartz Nodule)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: Creamy white to pale tan, Luster: Dull to waxy exterior, Crystal structure: Hexagonal/trigonal (if opened), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Creamy white to pale tan, Luster: Dull to waxy exterior, Crystal structure: Hexagonal/trigonal (if opened), Specific Gravity: 2.65
Formation & geological history
Formed as a silica-rich nodule within sedimentary rock layers, often limestone or shale, where groundwater deposits minerals into cavities. Most common in Paleozoic to Mesozoic era formations.
Uses & applications
Used primarily as decorative collector specimens, educational samples, and occasionally for lapidary work (slicing and polishing).
Geological facts
Geodes are often 'hidden' rocks that look like ordinary stones on the outside but can contain beautiful crystal linings inside. This specific specimen shows a botryoidal or vuggy texture common in silica nodules.
Field identification & locations
Identify by its light weight relative to size (if hollow) or its lumpy 'cauliflower' exterior texture. Commonly found in riverbeds or limestone quarries in the American Midwest and desert regions.
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