ge·ode /ˈʤiˌod/
  晶洞,異質晶簇
  Ge·ode n.  Min. (a) A nodule of stone, containing a cavity, lined with crystals or mineral matter. (b) The cavity in such a nodule.
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  geode
       n : (mineralogy) a hollow rock or nodule with the cavity usually
           lined with crystals