A hollow, usually spheroidal rock with crystals lining the inside wall.(noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "geode" in a sentence
"Of these strange noises there are many explanations, the most plausible being that they are caused by the explosion of the species of stone known as the geode, fragments of which are frequently found among the mountains."
"The geode has been a fairly open platform in the past – designed a STB around it in 2000 and had FreeBSD/linux ported to it fairly easily."
"The geode is a spherical and apparently solid stone, but when broken is found to be hollow and coated with crystals."