Diamond Head is a volcanic tuff cone on the Hawaiian island of Oʻahu. It is known to Hawaiians as Lēʻahi, which is most likely derived from lae plus ʻahi (tuna) because the shape of the ridgeline resembles the shape of a tuna's dorsal fin. Its English name was given by British sailors in the 19th century, who named it for the calcite crystals on the adjacent beach.