Send a comment on this item to LII: Send a comment on this item to LII staff, who on weekdays will usually reply within 24 hours. Geodes: Small Treasure Vaults in Illinois Illustrated fact sheet about these irregular, roughly spherical geological formations that are lined with mineral crystals. Describes the makeup of a geode and theories about geode formation. From the Illinois State Geological Survey. http://www.isgs.uiuc.edu/maps-data-pub/publications/geobits/geobit3.shtml Asterisk * indicates required field. Your Name Your Email Address * We will not sell or provide your email address to anyone else. Comment * Enter the verification code as it is shown in the box below. This helps prevent automated submissions. *