In the world of seabed geology, if a sulphide deposit is massive, it is not necessarily big, but formless and rich in metals. As it happens, seafloor massive sulphides are also huge—at least they were until recently. The collapse in commodity prices last year has diminished them a bit, but many expect their popularity to recover. The excitement arose because oceanographers had started to find these mineral-rich deposits on the network of submerged mountain ranges that run along the seabed between continents. Such ridges occur where the great plates of the Earth’s crust are spreading apart, and the seafloor holds formations of hot, volcanic rock. All this is of great interest to Anglo American and De Beers, among others.