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The Making of a Geode

Geodes are incredible feats of nature, what appear to be simple plain rocks, when cracked open contain gorgeous crystalline structures. There are seven (7) main types of Geodes and you can learn about those in our blog on Geodes.


Where Are Geodes Found?

Geodes can be mined in many different locations around the world, but are more frequently found in deserts, volcanic ash beds, and regions containing limestone.

Rock hounds in North America can hunt for Geodes in many locations in North America including Alberta, Saskatchewan, Ontario, California, Arizona, Iowa, Utah, and Nevada. Check out your local rock hunting clubs for tips on where to find deposits in your area.


Formation of Geode

Geodes form in both igneous and sedimentary rocks types. There are two basics steps to the formation of the Geode:

  1. A hollow cavity is formed in the rock.

  2. Minerals precipitate out of a groundwater forming crystals on the walls of the cavity.


Types of Geodes


  • Volcanic Geodes The most widely known and sought-after geodes are those formed in areas of volcanic activity. Voids in basaltic lava flowed and are infilled by agate, quartz, opal, and other material delivered by hydrothermal water or groundwater. The gases were trapped in the voids and were unable to escape prior to the lava hardening and the surface crusting over.

  • Sedimentary Geodes Geodes formed in sedimentary rocks are also formed as a result of trapped gases but are usually found in limestone, dolomite, or calcareous shale. The presence of shells, tree branches, roots, and other organic materials result in the creation of void as these materials often decay and a layer of minerals begins to form within the rock formation. The cavities can be filled with quartz, opal, agate, or carbonate minerals. These cavities are typically smaller than those formed within the geodes formed in volcanic rocks.

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