Geodes, Crystals Living in Their Own Little Worlds

     For as long as I have known about them, geodes have always captivated me. Sometimes a geode may contain hundreds of little shimmering crystals that might never have seen the light of day until you broke open their rocky confinement. My dad once said that crystals inside of a rock, like a geode, are like their own little world. Interestingly, the word geode comes from the Greek word geodes, which means “earthlike.”
     What are geodes? A geode is simply a hollow rock that is filled with crystals. Think of a basketball that has been inflated and filled with salt water. After a while the salt crystallizes on the inside of the basketball, thereby forming a lining on the sphere's interior. This is the way that geodes are formed, only the lining takes place inside of a hollow rock and with different crystals. Some of the most common minerals that make up the interior of geodes are: quartz, pyrite, calcite, barite, gypsum, strontianite, and a group of minerals called “zeolites.” Geodes are famous for being spherical (ball-shaped) but they can be stretched spheres or even shapeless. Geodes can be very tiny, golf-ball sized, baseball sized, basket ball sized, or even larger. Tiny geodes are called ocos. Some nicknames for geodes include: “eagle stones,” “thunder eggs,” and “echites.”
     According to science, geodes can be formed in two different ways; one by sedimentary activity and the other by volcanic activity. Volcanic geodes are thought to form when lava erupts from a volcano and a large bubble of gas is trapped inside of it (in mineral terms a gas bubble that is trapped inside of a rock is called a vesicle). This vesicle is then filled with mineral-rich water, which the crystals grow from. Geodes made by sedimentary activity are formed when natural acids dissolve a cavity into a rock. The crystals are then formed in this cavity by the action of mineral-rich water just like the volcanic geodes. Volcanic geodes are usually more spherical in shape and most often contain quartz and zeolites whereas the geodes formed by sedimentary activity are usually oddly-shaped and contain the other minerals listed above.
     Geodes do not serve many technological uses. If any of the minerals found inside of them do, I would assume that it is more cost effective to get them from sources other than geodes. Geodes are sometimes sliced into very thin sheets, which are used in jewelry making. Geodes are used mainly as decorative pieces and many mineral collectors like to collect them.    
     Geodes are found in many places throughout the world (in fact, I once found one on my grandmother’s property here in Michigan.) Some of the best geodes come from places like: Western Sahara, Morocco, Germany, Oregon, and Kentucky. Very large geodes can be found in Iowa, Missouri, and Illinois, and  geodes both large and small that are filled with purple amethyst crystals can be found in Brazil and Uruguay.
     Geodes interest me for a number of reasons. The beautiful crystals inside of them, their semi-complex origin, and the interesting shape that geodes often assume make them simply stunning. Geodes can remind me of miniture caves filled with glittering crystals. And sometimes they do seem like their own little worlds!