Geodes are spherical and semi-spherical rock structures that appear like any other rock from the outside, but are different on the inside. They have an internal cavity that is filled with a variety of minerals. The presence of different valuable minerals inside makes them look attractive. Therefore, these rocks are one of the most sought-after geological structures that professionals and collectors alike strive to acquire.
Natural Formation of Geodes
The formation of these special stones sounds like a tale of magic realism. Hollow cavities inside geodes are made when they take the shape of rocks from cooling magma or lava. Cavities are made inside rocks when a bubble of water vapor or carbon dioxide is formed in the flowing lava.
Cavities can also be made underwater when lava cools down to solidify in water. The outside surface of the melted magma solidifies before the inside. The liquid lava trapped inside causes the newly solidified crust of rock to leak. Once all the liquid has leaked out, a hollow space is left inside.
After the cavity is formed inside the geodes, the treatment of mineral-rich groundwater starts. Water accumulates a thin layer of minerals inside the cavities by seeping through porous rocks. It is imperative to mention that the process of mineral accumulation take a lot of time. The buildup of minerals gets transformed into crystals and this can take thousands of years. Some large crystals can take even few million years to grow into their final shape.
Geodes are special and rare geological structures and cannot be found in every rock formation. They are usually found in those areas where rocks are formed in a peculiar geographical environment.
Most geodes deposits are found in:
- Stratified volcanic deposits of tuffs and basalts
- Sedimentary carbonate deposits of dolomites and limestone
Small amounts of geodes can be extracted from some other rock formations as well.
Which Minerals Stones are Present in Geodes?
Not all geodes are lined with the same type of mineral residue. However, tiny quartz crystal and agate are mostly found inside geode cavities. But there are geode deposits that are lined with more precious minerals.
Purple amethyst, white calcite crystals, pink rhodochrosite, opals with spectacular play of color and colorful agates are also found inside some rare geodes. Geodes don’t have a definite size. Their size can vary from few centimeters to several meters.
Utilities of Geodes
Until they are unopened, there is no general interest in these stones. However, when they are opened and the inner lining of these stunning minerals becomes visible, then they become the center of attention for many reasons.
After determining the quality of minerals present inside, there are some geodes that are sold in auction and with astounding price tags. The price of rare geodes can easily race up to five digits. Affluent people with a hobby of precious stone collection take interest in those collector quality geodes.
Geodes: Decorative Tools
Large pieces of geodes that are mostly lined with agate and quartz are cut into small blocks and pieces with flat base to produce desk sets, clock faces and paperweights. Geodes used to make those economical products are abundant in nature and contain less striking agate and quartz colors like gray and white. These small geode units are often dyed and polished with vibrant colors to make them more appealing for customers.
Fine grade geodes (rocks lined with amethyst) are cut into different artistic shapes and used with weighted base or stand to be used as items of décor in residential and office spaces.
Beware of Fake Geodes
If you are paying a hefty amount for geodes, then beware. Fake geodes are also available in the collectors market. Highly skilled con artists line actual mineral stones inside pottery structures, which looks very identical to the original geodes.
Geode Sites in the United States
Lake Superior Agate
Located in the state of Minnesota, this lake is a buildup of agate that fills the cavities of basalt. It has formed in billions of years. Most of the geodes have eroded mineral linings, however some stones still contain linings of crystalline quartz and agate of orange and red shades due to higher amounts of iron impurities in the lined minerals.