Did the Black Stone descend from the sky, or is it a stone like any other, and what is the purpose of its placement in that particular location, and is it the Qiblah for Muslims in their prayers?

Allah has singled out the Black Stone for kissing and touching by those performing tawaf (circumambulation) when they are able. If not possible, then by pointing to it while saying "Allahu Akbar" when parallel to it. A Hadith with a weak chain of narration states that it descended from Paradise.