Composition
The silicon and oxygen elements that make up rock crystals are formed together into a tetrahedron. Each oxygen atom is shared between two tetrahedra, making the framework have the formula SiO4 and the overall material formula of SiO2.
Appearance
Rock crystals are colorless and generally clear, although some are smoky colored due to aluminium exposure. This smoky color can be artificially created by exposing the quartz to high levels of radiation.
Shape
One major feature of rock crystals is their tendency to develop into horizontal hexagonal prisms that lead into six-side pyramids. Sometimes these formations do not develop correctly, creating other shapes of crystals.
Potential
According to a natural healing organization, Charms of Light, rock crystals have a number of healing properties. They amplify energy and thought as well as give balance and revitalization in one's life.
Fun Fact
According to the ancient Greeks, rock crystals contained properties of ice. They believed that the crystals formed high in mountains and froze to such a degree that they wouldn't melt.