Quartz is one of the most common minerals in the Earth's continental crust and is made up of silica. A bed is a common form, particularly for varieties such as amethyst, where the crystals grow up from a matrix and thus only one termination pyramid is present. A quartz geode consists of a hollow rock (usually with an approximately spherical shape) with a core lined with a bed of crystals. The Greeks believed that natural quartz was made of ice frozen at very very low temperatures. All the ancient culture as always linked this crystal with therapeutic and magical powers that were able to keep away demons and sickness and to bring strength and energy. Natural quartz spheres were used to read the future.