Diamond Head is a volcanic tuff cone on the Hawaiian island of Oʻahu and known to Hawaiians as Lēʻahi. The Hawaiian name is most likely derived from lae (browridge, promontory) 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 mistook calcite crystals on the adjacent beach for diamonds.