"Geode" comes from ancient Greek "Gêodês", which means "Earth-like".
Geodes are rocky cavities lined inside with crystals as well as other minerals that usually have easily distinguishable shapes and defined faces.
Most of these crystals are clear quartz and its varieties such as amethyst, but they can also contain crystals of galena (the main source of lead) and other minerals such as calcite or celestine.
Its rough exterior can be made of different minerals such as basalt (cooled and solidified lava) and other minerals depending on its formation. It can also be made of the same mineral that covers its inside.
It is not really a mineral in itself but a compound of magmatic, crystalline and/or sedimentary formations. Its shape is vaguely spherical.
Their formation occurs in different ways.
When its origin is volcanic, a lava bubble solidifies within which silicates or carbonates are deposited covering the internal surface. Water and other liquids percolate through the exterior surface, which allow the formation and growth of crystals.
Its origin can also be sedimentary, which occurs when mineral sediments are deposited inside a round cavity. Mineral, liquid and/or gaseous materials crystallize due to the action of a set of conditions such as temperature changes, infiltration of other minerals and erosion.
Sometimes it is called "the stone of the eagles" since in some mountain ranges where it is present, such as in the Alps, eagles could use large geodes as a nest.
It was also called "Lapis Renalis" or kidney stone, due to its external shape and the emptiness inside that reminds us of a missing kidney.
In Bristol, England, a kind of "gold rush" began when dolomite geodes were found containing quartz so pure that it looked like diamonds. Due to this confusion they are known as Bristol diamonds.
In Somerset, also in England, they are so common that they are called "potato stones".
Unknown miniature worlds until opened, geodes spark imagination and inspiration. It is a compound mineral that has the effect of the crystals it contains.
An amethyst geode has the virtues attributed to amethyst, that is, it soothes and purifies while helping to combat addictions of all kinds.
A clear quartz geode synergizes with other gems and crystals, amplifying their power while purifying them.
They are found around the world but many geodes come from Brazil, Uruguay, Namibia and Mexico.
They are also found in various parts of the United States and it is the official stone of the state of Oregon.
They are difficult to extract whole and their content is unknown unless they come from a known deposit.
Not all geodes are hollow; the varieties that are filled on the inside are called "nodules". Some examples of nodules are agate and flint.
There are geodes so large that they are considered caverns or caves. Some are tourist sites such as the Crystal Cave in Ohio, United States with its celestite crystals and the giant Geode of Pulpí in Spain and its gypsum crystals. In both geodes the crystals can measure over 3 feet (1 meter) in length.
There is also the Cueva de los Cristales in the Naica mine in Chihuahua Mexico, however it is still in operation. Its access is very complicated as it is located almost 1000 feet (300 meters) underground besides once inside the humidity is around 80% and temperatures vary between 111°F and 132°F (44°C and 56°C).
This cave represents the geode with the largest crystals in the world, made of selenite, some exceeding 32 feet in length (10 meters) and weighing more than 50 tons.