Rhyolitic geode. Cut surface of a geode displaying the host rock rhyolite (green),chalcedony (blue- white) and haematite (red). Geodes form when a hollow in a rock becomes filled with mineral crystals that grow inward to the centre of the hollow. Rhyolite is a volcanic rock formed by the cooling of lava on the Earth's surface. Chalcedony is a term for many cryptocrystalline quartz (silicon dioxide) gemstones,including agate. The colours are derived from impurities in the mineral. Haematite is a form of iron oxide. This geode came from the Esterel region on the Mediterranean coast in France | |
Licence : | Droits gérés |
Crédit: | Science Photo Library / Wiersma, Dirk |
Taille de l’image : | 3720 px × 4728 px |
Model Release : | Non requis |
Property Release : | Non requis |
Restrictions : | - |