ChemGuide.co.uk explains Ionic bonds, "Electrons are transferred from one atom to another resulting in the formation of positive and negative ions. The electrostatic attractions between the positive and negative ions hold the compound together."
Essentially it is the balancing of positive and negative attractions when one atom steals the electron of another atom, and the atoms themselves are then bonded by those resulting positive and negative forces.
TheFreeDictionary.com defines an Ionic Crystal as, "A crystal in which the lattice-site occupants are charged ions held together primarily by their electrostatic interaction."
Ionic crystals grow out of ionic bonds. There are many types of Ionic crystals that occur naturally in the world. The most common Ionic crystal is salt. Ionic bonds are weak bonds because they rely on electrostatic interaction, rather than actually sharing an electron as is the case with covalent bonds.
W. R. Salzman of the Univsersity of Arizona's Chemistry Department offers the following list of ionic crystals with their definition.
"NaCl is an ionic crystal. It consists of a regular cubic array of alternating sodium and chloride ions. The chlorine ions are larger than the sodium ions." NaCL is more commonly known as salt.
"CsCl is an eight-coordinate crystal because each ion is surrounded by eight ions of the opposite charge." Cesium Chloride is less common, and is generally used in the laboratory.
"ZnS is an example of a four-coordinate crystal." Zinc Sulfide is used in infrared technologies because it emits light.
Ionic crystals are used in a variety of applications ranging from your evening meal to a soldier's night vision goggles. This is only a few examples of ionic crystals.
The most common example of an ionic crystal, NaCl, is more commonly known as salt. Salt dissolves readily into water because of the "weak" bonds between sodium and chlorine. Charles E. Ophardt of Elmhurst College explains that "If the attractions for the ions by the polar water molecules are the strongest, the crystal will dissolve. This is the situation in sodium chloride."
Ionic crystals are purported to posses mystical healing properties. AncientIonicCrystal.com says, "Salt Crystals have been known to help increase negative ions in the air." Their presence in a room reportedly impoves the ionic charge of the air and contributes to the overall fengshui of a room. These claims are not supported by science. Again, take them with a grain of...salt.