Crystal Clear with Crystals

A crystal or crystalline solid is a solid material whose constituents, such as atoms, molecules or ions, are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macroscopic single crystals are usually identifiable by their geometrical shape, consisting of flat faces with specific, characteristic orientations. The scientific study of crystals and crystal formation is known as crystallography. The process of crystal formation via mechanisms of crystal growth is called crystallization or solidification. Examples of large crystals include snowflakes, diamonds, and table salt. Most inorganic solids are not crystals but polycrystals, i.e. many microscopic crystals fused together into a single solid. Examples of polycrystals include most metals, rocks, ceramics, and ice. A third category of solids is amorphous solids, where the atoms have no periodic structure whatsoever. Examples of amorphous solids include glass, wax, and many plastics. Crystals are commonly recognized by their shape, consisting of flat faces with sharp angles. These shape characteristics are not necessary for a crystal—a crystal is scientifically defined by its microscopic atomic arrangement, not its macroscopic shape—but the characteristic macroscopic shape is often present and easy to see. Ice crystals are formed when water from the Earth evaporates into the air and becomes a gas called water vapour. The water vapour becomes clouds and then freezes and falls back down to earth as snow. Ice crystals can also form as frost on windows and on the ground when the air has a lot of moisture (water vapour) and the temperature is below freezing. Some types of crystals are formed from melted rock in the earth. When the hot rock cools gradually, it will sometimes form crystals. Geodes are round rocks that are formed when bubbles are trapped in the melted rock. As the bubbles cool down, crystals grow inside of the bubble of rock!