Crystal
From Simple English Wikipedia, the free encyclopedia

Quartz crystal
A crystal is a solid which has its element molecules (or atoms) arranged in a special way. In a crystal, the molecules are arranged in a repeating pattern. Well-known substances that have crystals are table salt or Quartz. Sometimes pressure needs to be applied to the substance, so it forms crystals. Different substances form different types of crystal. With table salt, the crystals are like cubes; with other substances the form of the crystal may be different.