Black sand is sand that is black in color. One type of black sand is a heavy, glossy, partly magnetic mixture of usually fine sands containing minerals such as magnetite, found as part of a placer deposit. Another type of black sand, found on beaches near a volcano, consists of tiny fragments of basalt.

Magnetite is a mineral and one of the main iron ores, with the chemical formula Fe2+Fe3+2O4. It is one of the oxides of iron, and is ferrimagnetic; it is attracted to a magnet and can be magnetized to become a permanent magnet itself. With the exception of extremely rare native iron deposits, it is the most magnetic of all the naturally occurring minerals on Earth. Naturally magnetized pieces of magnetite, called lodestone, will attract small pieces of iron, which is how ancient peoples first discovered the property of magnetism.