Geode or druse is a hollow or partially hollow, globe-shaped bulb that is covered on the inside with crystals. Usually geodes between 2.5 and 30 centimeters wide, but this can vary greatly. They are found in sedimentary rocks and are sometimes very expensive. A geodesic is composed of a thin but strong outer layer of silicates, usually filled with a layer of quartz crystals such as amethyst or smoky quartz, but it may be a rutile or calcite in located. There are also copies of which contains the cavity water. They would have been created as "bubbles" in the liquid magma that rose into a crater pipe during an eruption. Like bubbles in boiling milk gathering themselves under on the milk-forming membrane, so keep stabbing bubbles in the magma. These gas-filled voids remain after solidification of the magma existence and are filled with saturated mineral solutions. Geode occurs when a layer of silica in a guest room, usually a fossil cavity in the rock. The minerals in the water, that runs along the hardened outer shell, form crystals in the silica layer. In the cavities grow slowly crystals. Agate is formed in the same manner. Weighs one geodes and compares it the lightest weight than its weight can sometimes contain fine crystals. Geodes be cut with special pliers or broken in half to make the interior visible.