Mandalas transmit positive energies to the environment and to the people who view them. They are believed to effect purification and healing.
Mandala was introduced by the Lord Buddha himself and there are many different designs with different purposes. Generally, it is created using colored sands.
However, I have found 1.5 m diameter Stone Mandela of around 30 cm thick at Bodhgaya. It is located on the right side after exiting Mahabodhi Temple. There are few artifacts shops on that way. At the end of the shops you will find this beautiful Mandela housed in a single room.
You need to look carefully to find out the Mandela lines and print. At the periphery you will see Chain of Dorje symbols.
I prayed and received blessing from it. No doubt I am blessed with positive energy.
So next time when you visit don't forget to visit such rare Kalacharka Mandela.