Dalekanium

Dalekanium — also spelt Dalekenium — was the metal of which Dalek casings were made. (DAN: The Humanoids, DW: The Dalek Invasion of Earth and others)

Abilities
It was bulletproof and immune to most lasers and bombs, making a Dalek hard to defeat. Dalekanium could attract gamma radiation. Dalekanium panels were attached to the Empire State Building in 1930 to attract gamma radiation, which would introduce Dalek DNA into humans that the Cult of Skaro had captured. (DW: Evolution of the Daleks)

Dalekanium was vulnerable to Nitro-9 and to anti-tank rockets. (DW: Remembrance of the Daleks) as well as Dalek gunstick fire. (DW: Victory of the Daleks)

Metalert was a reinforced type of Dalekanium. The casing was infused with Flidor gold and sap from the extinct Arkellis flower. The rarity of these substances meant that only Dalek Sec used this substance. (DWF: Birth of a Legend)

Dalekanium was a good conductor. (VG: City of the Daleks)

Source
Venusian mineralogist Jeff Stone once claimed that Dalekanium was only found on Skaro, indicating it was a natural, rather than synthetic, substance. (DAN: The Humanoids)

Behind the scenes

 * Dalekanium — or as it was originally known, Dalekenium — was the earliest concept from spin-off material to make its way into the television programme. It debuted in 1964's The Dalek Book.