Element 115

The is one of the four crystal Meteorite Artefacts found in Tomb Raider III. It was fashioned from a meteorite by Polynesians, that impacted upon Antarctica many years ago.

Taken from Antarctica by one of the sailors from the HMS Beagle to North America, it somehow was obtained by the U.S. Government, and it resided in Area 51 before Lara stole it.

Powers
The powers are not unknown, we know that element 115, is a super charged adom, with enough energy to power many electric devices at once, and in zombies it's an actual reference as it generates the power to turn on the electricity and generates a upgrade for the weapons, which 115 supplies ammo for.

Trivia

 * Element 115 has also appeared in the game Call of Duty: World at War's Nazi Zombies mode, as the power that created the zombies.