geode

 
Pronunciation: /ˈdʒiːəʊd/

noun

  • a small cavity in rock lined with crystals or other mineral matter.
  • a rock containing a geode.

Derivatives

geodic

Pronunciation: /dʒiːˈɒdɪk/
adjective

Origin:

late 17th century: via Latin from Greek geōdēs 'earthy', from gē 'earth'