mineral
Quartz geode
Quartz (SiO₂), with a chalcedony/agate rind
AI-generated identification · may be incorrectWhite to gray, glassy-to-dull quartz crystals lining a hollow cavity; Mohs hardness 7, trigonal crystal system, no cleavage, and specific gravity about 2.65. The outer rind is gray-brown chalcedony, a microcrystalline form of quartz.
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Physical properties
White to gray, glassy-to-dull quartz crystals lining a hollow cavity; Mohs hardness 7, trigonal crystal system, no cleavage, and specific gravity about 2.65. The outer rind is gray-brown chalcedony, a microcrystalline form of quartz.
Formation & geological history
Forms when mineral-rich water deposits silica inside a cavity in volcanic rock or sediment; later quartz crystals grow inward. Geodes can range from recent to hundreds of millions of years old; this specimen’s age and exact source cannot be determined from the image.
Uses & applications
Commonly displayed or collected; cut geodes are used in décor and jewelry, while quartz is also important in glassmaking and electronics.
Geological facts
Geodes begin as hollow cavities, often formed by gas bubbles in lava, and develop crystal-lined interiors as minerals precipitate over time.
Field identification & locations
Identify by its rounded, rough exterior and hollow interior lined with inward-pointing crystals; quartz geodes occur worldwide, notably in Brazil, Uruguay, and the United States.
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