Crystals are in fact very common. Take a look around you when you sit down to dinner. Your metal knife is a crystal, as are your spoons, forks, and metal serving bowls. The ice in your cup is a crystal, as is the salt in your shaker. Your ceramic plates and bowls are also crystals. Interestingly, your "crystal" wine cups are actually one of the few items in your house that are not crystal. Looking into the kitchen, you see your metal fridge, your metal sink, your granite counter tops, your tiled floor, your plaster walls, and your electronic gadgets – all crystal. In fact, aside from glass and organic material such as wood, cotton, or bamboo, almost all solids are crystal. There are even some liquids that are crystal, such as in your iPod screen. In science, the word "crystal" describes a material that has an ordered spatial arrangement of its molecules. For instance, salt molecules line up in straight columns and rows when forming a salt crystal. Almost all metals, ceramics, salts, rocks, and semiconductors form crystals when in the solid state. Glass, on the other hand, has its molecules randomly distributed. Organic materials such as wood and cotton have highly complex biological structures on the molecular level and therefore do not have the simple repeating patterns characteristic of crystals. But simple organic molecules, such as sugar, do form crystals if they are concentrated and solidified.