Geodes are more or less spherical or egg-shaped rocks containing a hollow cavity which is lined with crystals. They form in both igneous and sedimentary rocks.

What kind of rock is a geode?

A geode (/ˈdʒiː. oʊd/; from Ancient Greek γεώδης (geṓdēs) 'earthlike') is a geological secondary formation within sedimentary and volcanic rocks. Geodes are hollow, vaguely spherical rocks, in which masses of mineral matter (which may include crystals) are secluded.

Are geodes metamorphic rocks?

Geodes are technically sedimentary rocks, since they are the result of the action of water. Geodes are formed when cavities in a host rock (which may be sedimentary or igneous) become lined with a durable mineral, often a variety of quartz. The term geode usually refers to rounded nodules with hollow centers.