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 named it for the calcite crystals on the adjacent beach.

Diamond Head is part of the system of cones, vents, and their associated eruption flows that are collectively known to geologists as the Honolulu Volcanic Series, eruptions from the Koʻolau Volcano that took place long after the volcano formed and had gone dormant. These eruptive events created many of Oʻahu’s well-known landmarks, including Punchbowl Crater, Hanauma Bay, Koko Head, and Mānana Island in addition to Diamond Head.

Diamond Head, like the rest of the Honolulu Volcanic Series, is much younger than the main mass of the Koʻolau Mountain Range. Source: Wikipedia.org