Rhyolitic geode. Chalcedony (red) and crystals of quartz (central hollow),inside rhyolite rock (the surrounding round structure). This geode has been cut open to show its internal structure,and polished to improve its appearance. A geode forms as layers of the mineral silica (silicon dioxide) precipitate from liquid onto the sides of hollows in rock. An amorphous form of silica (chalcedony) forms the banded layers seen,with impurities for colouring. The final inner layers that precipitate are crystalline silica (quartz). Rhyolite rock is volcanic. Volcanic rocks often contain such spaces that are suitable for forming geodes. This sample is from the Esterel region of France | |
Lizenzart: | Lizenzpflichtig |
Credit: | Science Photo Library / Wiersma, Dirk |
Bildgröße: | 3827 px × 4615 px |
Modell-Rechte: | nicht erforderlich |
Eigentums-Rechte: | nicht erforderlich |
Restrictions: | - |