Geodes are essentially hollow, spherical to egg-shaped masses of mineral matter. They are geological secondary structures that occur in certain sedimentary and volcanic rocks and are themselves of sedimentary origin formed by chemical precipitation. Geodes form by either one of two processes:
  • by the filling of vesicles (gas bubbles) in volcanic to sub-volcanic rocks by minerals deposited from hydrothermal fluids or
  • by the dissolving of sedimentary nodules or concretions (that were deposited at the same time within the rock formations in which they are found) and partial filling by the same or other minerals precipitated from groundwater or hydrothermal fluids.
Each geode is unique in its composition which is only discovered when it is cracked or cut open because its rough exterior gives no indication of the secret structure within. The size and formation of the crystals and different hues within the crystals make each geode special.

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Item # Item Description Price
S407 CH
"Thunder Egg" or Choya Geode - These nice almost 4-inch diameter specimens FROM MEXICO can be cut or broken for display. Inside each one is some form of quartz such as crystals and agate. Just like a box of Cracker Jacks; always a surprise inside. $42.00

S407 BV
Bravos Geode - These 1 inch to 1.5 inch diameter geodes are from Mexico. They contain chalcedony and small quartz crystals. The chalcedony fluoresces lime green under shortwave ultraviolet light. Small Bravos

Medium Bravos
S407 TC
Trancas Geode - These gray-skinned geodes from Mexico that range from 1.5 inch to 3 inches in diameter. Use a hammer to break your own and discover the crystals that have formed inside. Small Trancas

Medium Trancas

Large Trancas
S407 DG
Dugway Geodes are from Dugway, Utah. They are found in a volcanic tuff located in the Dugway Mountains. They come in a variety of shapes, sometimes with two or more joined together. The size range on our Dugway are between 2.5 and 3.5 inches. They all contain some form of silica dioxide generally in the form of chalcedony. Dugways fluoresce a brilliant-lime green color in shortwave ultraviolet light. $15.00

Caution CAUTION: ALWAYS PROTECT YOUR EYES. Geodes can be broken by striking them with a hammer or similar heavy object. When breaking a geode, wrap it in a towel or place it in an old sock before striking it. Calcite geodes are much softer than quartz geodes and should be struck more lightly to avoid shattering.