No, this is not the
Sunstone.
Item from Chrono Trigger. The Sun Stone is a jewel the size of a man's head, capable of storing sunlight in it and channel it as pure energy. It was probably used to air the construction of the Mammon Machine and the Ocean Palace.
When found by Crono and friends in the year 2300 AD, it has been completely drained of energy and turned into a Moon Stone. In this state, only the energy of 6502.3 thousand years of straight sunlight can bring it back to its shining glory.
Expert scientists can use the energy of the Sun Stone for various means, including beams of devastating power. Melchior was able to combine the Rainbow Shell and the Sun Stone (Yes, Chrono Trigger has a lot of special stones) to create Crono's ultimate blade, the Rainbow.