Fairy Grottoes
Geodes Are Humble Rocks; They Do Not Flaunt Their Beauty.
Inside the most pedestrian rocks, miniature cathedrals may be awaiting discovery. Geodes conceal crystal palaces hidden for millenia; you need only know where to look.
Although the actual origin of these spectacular treasures is largely unknown, there are theories that give us a peek at the forces that brought them into being. The caprices of nature often leave even the foremost scientists at a loss, and geodes still retain a bit of mystery that has not been solved yet. They are so named because of their (usually) spherical shape, and they vary in size from the customary two- to three inches to the mind-bending twenty-five foot geode found in Spain.
The Two Most Likely Theories of Geode Formation
The most likely explanation for these rocks is revealed by their natural location and mineral make-up. There are two categories of geodes: lava geodes and dolomite geodes.
Lava-formed geodes are believed to have been formed by bubbles in the molten rock, around which a surface of cooling rock formed a shell-like exterior. Water would have seeped through cracks in these cavities, or filtered in through the surface of the stone. As the rocks cooled, the minerals in the water crystallized and formed the lacy structures inside the hollow crust.
Dolomite geodes are thought to have been formed in a slightly different way, because of the regions in which they are found. Sediment build-up in shallow seas may have formed hard nodules in the limestone, which is abundantly filled with calcite. Salty sea-water seeped through the sediment and dissolved the calcite, creating a chemical reaction that in turn created anhydrite and dolomite.
As the water interacted with the dolomite, it became slightly acidic and dissolved the outer surface of the anhydrite. Quartz crystals carried in the water began to collect and grow into the cavities formed by dissolving anhydrite, growing towards the center of the concavity; the only direction possible for their growth.
Crystal Formation
Crystals are formed by the cooling process of the rock, and the chemical make-up of the crystal decides the shape of the crystal shafts. Also playing a part in the formation are the confines in which they are forced to develop, and the speed at which they cool. The more slowly the rocks cool, the longer the crystals will be.
Nature provides us with endless sources of interesting and amazing quirks that stimulate our imagination or gratify our sense of beauty. Geodes furnish us with a sense of irony in that they are actually quite ugly at first blush, and only by violence do we find the beauty within.
