Crystals have a variety of shapes, colors and sizes, and they normally feature distinct geometric patterns of parallel or reticulated planes, or facets. They vary in size from a few millimeters to several feet in length, and they often resemble cubes, needles, spheres or elongated columns.
Crystals may be clear and transparent or brightly colored and iridescent. Crystals form when liquids and solutions solidify and the atoms bond to form highly ordered and repeated patterns called lattices. They vary in shape, size and color according to the substance that forms them and the conditions under which they form, such as temperature and pressure. Some crystals, such as diamonds, rubies and sapphires, form deep within the earth, while others, such as snowflakes, form in the atmosphere.