Most substances will form a crystal if allowed to solidify under the right conditions. Usually the slower the process happens, the more likely it will be that the molecules will find their proper place in the growing crystal's structure. Water will form crystals under several conditions. Snowflakes are examples of water crystals which have formed from water vapor in the air and then assembled themselves into a flat, lacy mass. Although snowflakes are the most spectacular form of water crystals, the crystals form whenever ice occurs.
Sugar is an example of common organic crystal.
While to the naked eye it may look identical to table salt, examination with a microscope, or even a good magnifying glass, will reveal that the two crystals are of different shapes because they belong to two different crystal systems. A section of petrified wood. The word crystal comes from the Greek krystallos , which means ice. The Greeks found beautiful quartz crystals in the Alps mountains and believed that they were a form of water frozen so hard that they would never thaw. Rock crystals were sometimes sculptured into shapes.