Pele's Curse is the belief that anything natively Hawaiian, such as sand, rock, or pumice, will effect bad luck on whoever takes it away from Hawaii.
The general consensus about the legend's genesis is this: a disgruntled park ranger, angry at the number of rocks that were being taken from the islands by visitors, said that Pele would curse them with bad luck should they take anything. The myth has caught on and every year countless tourists send these back in order to escape the awful luck that Pele has caused them.
Although the legend itself is probably of twentieth-century origin, the removal of rocks as souvenirs is frowned-upon by Hawaiians, and it is illegal to remove minerals from a U.S. national park.