Geodes are round rocks which contain a hollow cavity lined with crystals. These rocks have a chance of containing various gemstones and Minerals, which can be either donated to Gunther or turned into bars (depending on what is inside the Geode.) Geodes can be broken opened by Clint for a fee of 25g per Geode.
Based on how deep into the Mines you hunt, you can find an assortment of various types of Geodes.
A basic Geode takes the appearance of a rugged spherical stone. These geodes can be easily found from stones on your farm, or any level in the Mines.
Frozen Geodes, found around the mid-floors of the Mines (Floors 60-80) take the appearance of a triangular stone with a bluish-green tint.
Omni Geodes, found within the lower levels of the mine (80-100, rarely found around 70-80) appear as a cluster of stone with various colorful specks.
The first time
The first Geode you will mostly find at your farm, when you begin to break the rocks there.
When you do this a window is opening with the text:
You found a 'Geode'! the local blacksmith can break it open for you.
Who knows what might be hidden inside?
Stone, Coal, Iron Ore (1-5), Copper Ore, Amethyst, Topaz, Granite, Sandstone, Slate, Quartz, Earth Crystal, Calcite, Thunder Egg, Nekoite, Limestone, Jade, Jamborite, Dwarf Helmet (Artifact), Alamite, Petrified Slime, Clay, Mudstone, Orpiment, Celestine, Malachite, Jagoite
(Several other contents. Please add as you find more!)