From the article F15Eagle linked (which makes a heck of a lot more sense than Wikipedia), it's the black rock/meteorite that Muslims try to kiss while on their pilgrimage to Mecca. When it broke apart back in the 600sAD, they set the rock in silver. It is usually placed at one of the cornerstones of the Kaaba:
However, the silver thing containing the rock is removable for cleaning, which the tribe in charge of maintaining the Kabaa does once a year. That's why there are people holding it in F15Eagle's original picture. In that picture, it truly looks like a bedpan, spittoon or bad mirror.