When Marco Polo heard it in China, he suspected evil spirits. When residents of Copiapo, Chile, heard it emanating from a sandy hill, they dubbed the peak El Bramador, for its roars and bellows.

One evening in 1908, a Namibian railway worker named Zacherias Lewala was shovelling railroad tracks clear of creeping sand dunes when he saw some stones shining in the low light. Lewala’s German ...