Geode
Two geodes, halved and polished.
are geological formations common to
Indiana, the
Keokuk area of
Iowa,
Kentucky,
Brazil and
Mexico. Essentially rock bubbles with internal cystal formations, the exterior of a geode is generally limestone or a related rock, while the interior contains
quartz crystals and/or
chalcedony deposits. Geodes work their way up to the surface of the earth crust's after millions of years.
Geologists do not yet have a widely accepted theory about how geodes are formed.