What You Do:

Practice developing and test hypothesis.

Learn about the formation of geodes.

Break open a geode to expose the crystal formations.

What You Need:

Geode ( 1 per student )

Goggles ( ~1 per 4 students, although you can do with as little as 1 )

Hammer ( ~1 per 4 students, although you can do with as little as 1)

Socks ( ~1 per 4 students, although you can do with as little as 1)

Plastic Bag ( 1 per student )

Geode Gems Worksheet, with Earth Science Crossword on Reverse (1 per student)

What’s Happening:

Geodes are rocks that are plain on the outside but can have beautiful crystals on the inside. In the Greek language, geode means “shape of the earth”, and geodes are round like earth or oblong like an egg. They can be a couple inches or several feet in size.

Geodes are created in the hollow areas of soil such as animal burrows or tree roots. They are also formed in the bubbles in volcanic rock. Over time, dissolved minerals seep into a hollow area and harden into an outer shell creating the geode. The minerals continue to form on the inside walls of the shell, growing towards the center. The most common dissolved mineral is quartz, but amethyst and other minerals are also found.

It can take hundreds of millions of years for the space inside a geode to be filled, and many geodes remain partly hollow. A geode which is completely filled with crystals is called a nodule. Agate-filled nodules are called thunder eggs.

Geodes can have many colors depending upon the type of crystal. Purple is a typical color for amethyst. Because crystals have flat, clear surfaces with many facets, they reflect light and have a beautiful sparkle.

Geodes are found throughout the world, and many are concentrated in deserts. Volcanic areas are a common place to find geodes. In the United States they can be found in California, Arizona, Utah, Nevada, Illinois, Missouri, Kentucky, and Iowa.