The Black Stone is a 30 cm (12 in) diameter stone embedded in a silver frame on a corner of the Kaaba (Arabic: cube) in Mecca. The Kaaba is the holiest place in Islam, located near the center of Mecca. Five times a day, Muslims around the world pray in the direction of Mecca. During the Hajj, a religious pilgrimage to Mecca, Muslims walk around the Kaaba seven times, beginning and ending at the Black Stone, which they kiss if there is an opportunity. Muslims are careful to point out that they are not worshipping the Black Stone or the Kaaba, just using it as a focus of prayer to God and the memory of Muhammad.
There are several legends and stories surrounding the Black Stone. According to Islamic tradition, the Black Stone fell from Heaven, God's way of showing to Adam and Eve where to build a shrine to make sacrifices to Him. In the process of Noah's flood, the altar and stone were lost, until Abraham, one of the earliest prophets, rediscovered the stone with the help of Archangel Gabriel and built a new altar there. Originally dazzling white, the stone turned black after millennia of absorbing the sins of pilgrims.
Because the Black Stone has not been tested in a laboratory, its makeup is unknown, though various visitors have proposed that it is an agate, basalt lava, piece of natural glass, or -- most popularly -- a stony meteorite. Though it is often called a meteorite, this identification is inconsistent with the stone's glassy appearance as well as a 951 CE account that said the stone could float on water. More likely, the stone is a tektite (molten silica ejected by a meteorite) or desert glass, a type of mineral created when an asteroid explodes in a thermal airburst and fuses together the underlying sand. If it is the latter, then a possible site of discovery may have been the Wabar craters in the Empty Quarter of Saudi Arabia, three craters covered in black glass, meteorite iron, and chunks of white sandstone.