I noted in a thread not long ago that the Meneltarma on Numenor often makes me think of the Kaaba at Mecca, so this is an interesting thread!
Now, is it my imagination or is there something in one of the texts which states that the walls of Orthanc were constructed of Obsidian? That's not from meteorites but is an Igneous rock formed by volcanic activity (and very nice, too). And Tolkien noted that the walls around Minas Tirith were black and of the same stone.
If someone can clarify or not about this that would be excellent.