
Geodes are formations that occur
in gas bubbles or vugs in sedimentary rock. Hydrothermal forces bring
silica solutions which crystalize into a quartz crystal cave, usually
starting as cryptocrystaline (tiny interlockedcrystals) or Agate, and
finishing with an interior of larger single crystals or Quartz. These
can be many colors, Amathyst, Citrine, Smoky Quartz. 



