Scion
Lara found the first two pieces in the Tomb of Qualopec in Peru, and the Tomb of Tihocan underneath a monastery in the Mediterranean. She also recovered the third piece from the Sanctuary of the Scion in Egypt. The Scion was destroyed by gunfire from Lara in Atlantis, but pieces of it remain in Lara's treasure vault.
Tomb Raider: Anniversary
The Scion will be returning to Tomb Raider: Anniversary in much more detail.
Nothing has been confirmed about it as of yet, but it is expected to have the same powers in the new game, since it resembles an important part of the first Tomb Raider storyline.
Powers
The powers of the Scion can mutate creatures into much more agile and ferocious beasts. It can increase muscle mass and capability. The Scion also powered the Great Pyramid that lay at the centre of Atlantis. The powers of the Scion allowed Natla to create a small army of mutated beasts from cocoons that lay within vast hatcheries in the Great Pyramid.