Geodes, nodules and vugs are rocks filled with various types of crystal.
Bowl-shaped rock halves lined with crystal are some of the most beautiful and intriguing objects in any rock or crystal shop. These rocks, called "geodes," are most commonly filled with quartz, but may also be lined with calcite or amethyst. Solid, crystal-filled geodes are called nodules. These may also contain agate, jasper or chalcedony. The less durable "vug" is another form of crystal-lined rock.
Geode Origins
Volcanic geodes begin with a bubble in the rock. As the surrounding covering hardens, water containing silica washes through the bubble and deposits minerals such as quartz, amethyst or calcite. Layers of crystal form over the course of millenia, when silica in the water cools at different rates. The same process takes place in sedimentary rock when animal burrows, mud balls or tree roots form a hollow space through which silica- and mineral-containing water passes.
Vugs
Vugs are similar to geodes but are less durable. According to the Geology Adventures website, shifts in the earth surrounding a vug can cause a partial collapse of the vug's outer walls, leaving the crystals in the core exposed and easily harvested by crystal collectors. The shifting of tectonic plates creates cracks that become partially filled with quartz, calcite and other minerals. Erosion may also cause the removal of mineral crystals, forming a cavity lined with the remaining crystals.
Finding Geodes
Although a collector can find a variety of geodes simply by walking into the nearest rock or crystal shop, it is also possible to dig for the fascinating crystal-filled rocks. Geodes may be found worldwide, especially in desert areas. In the United States, California, Utah, Arizona, Nevada and Iowa have a substantial supply of geodes. Safety glasses and a pick and shovel are essential tools for mining geodes, and a hammer is useful for breaking these treasures open.
Geode Uses
Because geodes contain crystals, practitioners who use crystals for healing consider geodes to be sources of healing energy. Geodes also provide a lovely focal point for meditation. Geodes create a dramatic display on a table or shelf, and are sometimes incorporated into the stonework surrounding fireplaces. Additionally, geodes make a beautiful addition to landscaping features and gardens.
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