The Black Stone is the eastern cornerstone of the Ka'ba, and is supposed to have been found by Ibrahim and Ishmael. Thought to be a meteorite, it is 30cm in diameter. In Islamic tradition, Muhammad was said to have kissed the stone, and today's pilgrims try to do the same if they can reach it. It was broken into pieces several centuries ago, and is now held together by a silver frame.
The explorer Richard Burton was one of the few non-Muslims to reach the Ka'ba, and he described the stone in 1853:
The colour appeared to me black and metallic, and the centre of the stone was sunk about two inches below the metallic circle. Round the sides was a reddish brown cement, almost level with the metal, and sloping down to the middle of the stone. The band is now a massive arch of gold or silver gilt. I found the aperture in which the stone is, one span and three fingers broad.