Tungsten (also called wolfram)  is a chemical element. It is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a distinct element in 1781 by the Spanish chemist and mineralist Juan José Elhuyar Lubize who isolated the mineral as a metal in 1783.

Tungsten cubes are utilized in (US) military, defense, and aerospace applications. Specifically, they are widely used in fragmentation devices. In fact, it is a fillment for fragmentation bombs and fragmentation artillery shells, that we consider designed as an anti-personnel munition for on the battle field. It looks that the Israelis use tungsten cubes against civilians.

Elmet is an US-based company that produces these fillment.

The image is illustrative.