what are geodes
GEODES. Like: Share: 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.eodes 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.