The Sankara Stones are based on similar stones called Lingam or Shiva-Linga which are quite commonly used in Hindu religion. A lingam is a representation of Shiva and used for worship in Hindu temples.
Indiana Jones and the Temple of Doom
The Sankara Stones are smooth stones with three lines across it that represent the 3 levels of the universe. The stones contained diamonds inside, which would glow when the stones were brought together. The stones could provide warmth and life, but the stones could also light on fire.
According to a centuries old manuscript, Sankara was a priest who climbed Mount Kalisa where he meets Shiva, the Hindu god. Shiva told Sankara to go forth and combat evil. To help him, Shiva gave him 5 sacred stones with magical properties.
Over the centuries, the stones were dispersed by war and sold off by thieves.
Two of the Sankara Stones were hidden in the catacombs underneath Pannkot Palace. They were hidden there by a Thugee priest when the British raided the temple.
Three of the Sankara Stones were found in the Indian village of Mayapore where it had brought happiness and prosperity to the village. These three stones were taken by the Maharajah of Pankot, who stole them when the people of Mayapore refused to worship the Pankot god. The Thuggees believe that once they acquired all 5 stones, they would be all powerful. When the sacred stone was taken, the village wells dried up, the river turned to sand, the crops were swallowed by the earth, and the animals laid down and turned to dust. There was also a fire in the fields and the women were crying in darkness.