DIRK WIERSMA / SCIENCE PHOTO LIBRARY DIRK WIERSMA / SCIENCE PHOTO LIBRARY
Geode interior. Quartz crystals lining the hollow inside a small geode (geodino). A geode forms when layers of the mineral silica (silicon dioxide) precipitate from liquid onto the inside of hollows in rock. The silica changes from an outer layer of chalcedony (amorphous or non-crystalline silica), with the layers becoming more crystalline towards the centre. Quartz is the crystalline form of silica, and forms in the interior of a geode. This geode has been cut open to reveal the interior. Colour in the silica is formed from impurities.
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