Rarer than any metal, any mineral, so rare that if you scan the entire earth, all six million billion billion kilos or 13,000,000,000,000,000,000,000,000 pounds of our planet, you would find only one ounce of it?
Self-defense is a common defense by a person accused of assault, battery, or homicide. The force used in self-defense may be sufficient for protection from apparent harm (not just an empty verbal threat) or to halt any danger from attack, but cannot be an excuse to continue the attack or use excessive force.
In some jurisdictions assault is defined as the threat of bodily harm that reasonably causes fear of harm in the victim while battery is the actual physical impact on another person. If the victim has not actually been touched, but only threatened (or someone attempted to touch them), then the crime is assault.