From the outside, geodes look like common rocks but upon opening them, they can take your breath away. People are amazed at geodes as they contain beautiful clusters of crystal. Thousands of tons of geodes are sold each year. They are used for jewelry, decor, even bookends.
Uruguay, Brazil, Namibia and Mexico are the world’s largest geode producers and have developed profitable industries mining for them. They collect geodes, prepare and export them worldwide.
Indeed, geodes sell rapidly as items of art and for science. During geode demonstrations at museums, crowds often produce cheers when a geode is opened. There is something special hiding beneath these rocks which look ordinary from the outside. But do you know how geodes are formed and where they come from? Find out more by reading on.
A geode is a spherical rock structure with mineral materials lining the cavity. It is made of tiny quartz crystals with gray and white agate. Some of the more common linings in geodes are calcite crystals and amethyst.
The outer wall is built with durable materials that are resistant to weathering versus the host bedrock. With this, the geodes can survive intact even if the surrounding bedrock deteriorates.
Rare geodes can be filled with opal, blue gem silica, or rhodochrosite. Furthermore, geodes can come in different sizes from one centimeter to a few meters.
Formation and Occurrence of Geodes
Geodes are not just formed anywhere. You can find them in clusters where rocks have formed because of a special geochemical environment.
Geodes can form in various ways. Most geode localities are stratified volcanic deposits and stratified sedimentary carbonate deposits:
- Volcanic Geodes: The most sought-after geodes are those which are formed near areas of volcanic activity. The voids are filled with opal, quartz, and agate delivered by groundwater or hydro-thermal water. The voids can be gases that failed to escape the lava. Then, the gas can be trapped in the lava which can produce a cavity when the lava solidifies.
- Sedimentary Geodes: These are usually found in limestone, calcareous shale, and dolomite. The opening of geode formations can be filled with gas. Tree branches, shells, roots, plus other organic materials can decay and leave the void. The cavities can be filled with agate, opal, quartz, and other carbonate materials. Sedimentary geodes are smaller in size than volcanic geodes.
Geodes can be collected easily whenever their host rocks have deteriorated. This occurs because dolomite, limestone, basalt and shale can weather quickly and easily versus quartz. When the host rock whethers away, geodes are left on the surface. They can be washed up by a stream or get stranded in the soil.
Thereafter, geodes can be easily found and collected. But there are some geodes which can be produced by mining the host rock. However, this method is difficult, very expensive and can often damage the geodes.
Geode coloration is caused by various impurities. For example, iron oxides can give rust hues to quartz.
Moreover, the color of a geode depends on the type of crystal inside and the agate layer. The majority of geodes have clear quartz crystals while there are those which have purple crystals. Others can have chalcedony, agate or jasper banding.
There is no easy way to know what’s inside the geode until you cut it open. But geodes from one area can have the same appearance and color. If the geode has very bright colors, most likely, it has been artificially dyed.
Geodes look like plain rocks on the outside but they contain treasures. The crystals inside contain calcite, amethyst or clear quartz. These treasures are being sold around the world to be used for jewelry and art.
Geodes are formed in both sedimentary and volcanic rock under various conditions. The most common theory is that geodes are formed inside an already existing rock. Groundwater with minerals fills the hollows in the rocks. Over thousands of years, the minerals precipitate out of the water which leaves a gel on the interior wall which hardens into rock.
There are many areas around the world where geodes are abundant. These deposits can support the activities of collectors while there are some which can support manufacturing industries. During rock shows, geodes will always captivate the public. They never fails to amaze because of their undeniable beauty.
World’s Largest Geode – FossilEra
Agate Geode with Quartz crystals – Wikimedia Creative Commons
Guest Author Bio
Michael has been passionate about fossils and rocks ever since he was young. As he grew up, Michael spent most of his time digging and studying these minerals. He often travels to different parts of the globe to find the most valuable fossils and rocks.
Michael shares his knowledge and passion with the world by submitting articles online. He believes that through these articles, he can inspire more people to appreciate the beauty and rich history of fossils and rocks.