Minerals - Geodes From Iceland Teigarhorn Nature Reserve Royalty-Free Stock Photography

Geodes are geological secondary structures which occur in certain sedimentary and volcanic rocks. They are themselves of sedimentary origin and are formed by chemical precipitation. Geodes are hollow, vaguely spheroid to oblate masses of mineral matter which may include crystals that form either by the filling of vesicles in volcanic to sub-volcanic rocks by minerals deposited from hydro-thermal fluids or by the dissolution of igneous nodules or syn-genetic concretions and partial filling by the same or other minerals precipitated from diagenetic water, groundwater or hydro-thermal fluids.