The geological structure of the island is important in relation not only to the relief features but also to its valuable mineral resources. Metamorphic and sedimentary formations are found extensively. The metamorphic rocks fall into two major groups, gneiss and schists, and serpentine. The principal outcrop of gneiss constitutes the Ignambi chain, about 40 miles long in the northeast part of the island. There are several main summits, of which Mt. Panie, 5387 feet, is the higest point in New Caledonia. On the seaward, to the east, the mountain chain slopes steeply to the coast with scarcely a break, and the streams that flow in its narrow valleys fall in a series of cataracts, one of the notable of which is at Tao. On the landward side, to the west, the descent is also steep, to the valley of the Diahot River. The mountain masses in the rest of the island show a confused series of peaks and ranges, not arranged in any major chain. The schists, hard and crystalline, occupy an area from the east-central part of the island northwest to the extreme north; their relief is extremely irregular and broken. The second group of metamorphic rocks, composed largely of serpentine, attains its chief development in the south of the island, though from there it extends in a series of progressively more isolated massifs to the extreme northwest.
Sedimentary rocks are confined to a zone a few miles broad extending along the west coast from the south of the island for about three-quarters of its length. They are the most important factors in the relief of broad, gently undulating plains, with some step-sided hills that do not reach a great elevation.
The metamorphic rocks of New Caledonia yield copper, gold, and argentiferous lead and zinc; the serpentine of the northwest and the southeast yields nickel, chrome, cobalt, and iron, and the sedimentary earths provide some manganese, antimony, and coal.