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Posted by on Nov 28, 2015 in Tell Me Why Numerous Questions and Answers |

What Are Geodes and How Do They Form?

What Are Geodes and How Do They Form?

Geodes are spherical rocks that contain hollow cavities lined with crystals. The name geode comes from the Greek word Geoides, which means “earthlike.” These unique rocks can be formed in a variety of ways.

In volcanic rock, geodes start out as bubbles. Geodes can form in areas far away from volcanoes, too. In sedimentary rock, geodes might start out as animal burrows, mud deposits, or even tree roots.

Over time, the air, mud, or tree roots create a hollow cavity within the rock, while the outer edges harden into a spherical shape. Every geode is unique, because each geode has a unique composition that is different from every other geode.

Once the groundwater begins to flow around and through these rocks it picks up a variety of minerals as it makes its way down from the surface.

These minerals, including quartz, amethyst, and calcite among others, become dissolved in the groundwater and then get deposited on the inside of developing geodes over long periods of time.

The only way to discover the beauty inside of a geode is to crack it open with a rock hammer or cut it open with a rock saw.

Geodes will vary widely in terms of their size, crystal formation, and colors. Some of the most prized geodes are those that feature rare black calcite or amethyst crystals.

Geodes can be found all over the world. Areas with the most geodes, however, tend to be deserts, volcanic ash beds, or areas with plentiful limestone.

Content for this question contributed by Tom Wade, resident of Cincinnati, Hamilton County, Ohio, USA