According to the Holy Prophet(sa), the black stone in the Ka’aba is one of the remnants of the stones that were showered from ‘heaven’. The ‘stones’ that came from ‘heaven’ (which we now understand were probably part of a meteor-showered in that area under the command of God) were used to build the very first house of worship of God.
Though it had obviously been revered and respected by the previous generations, it should be borne in mind that the Black Stone itself does not hold any spiritual significance at all. The pilgrim may touch or if he can approach near enough, kiss the Black Stone, which is an emotional gesture calling to mind the time when the Holy Prophet(sa) kissed it when he performed the circuit. The Holy Prophet Muhammad(sa) did this, not because of any sanctity attached to the stone, but as an expression of his emotion at the Ka’aba,