Editing Geode (section)

{{Short description|Hollow formation inside a rock}}
{{other uses}}
{{distinguish|Geoid}}
[[File:Geode inside outside.jpg|thumb|[[Quartz]]-filled geode, shown from inside (top) and outside (bottom)]]

A '''geode''' ({{IPAc-en|ˈ|dʒ|iː|.|oʊ|d}}; {{etymology|grc|{{lang|grc|γεώδης|italic=no}} ({{grc-transl|γεώδης}})|earthlike}}) is a [[geology|geological]] secondary formation within [[sedimentary rock|sedimentary]] and [[volcanic rock]]s. Geodes are hollow, vaguely spherical rocks, in which masses of [[mineral]] matter (which may include crystals) are secluded. The [[crystal]]s are formed by the filling of [[vesicular texture|vesicles]] in volcanic and [[subvolcanic rock]]s by minerals deposited from [[hydrothermal fluid]]s; or by the [[solvation|dissolution]] of syngenetic concretions and partial filling by the same or other minerals [[precipitation (chemistry)|precipitated]] from water, [[groundwater]], or [[hydrothermal]] fluids.