Coincidence?

[Eönwë]

Originally Posted by Lalwendë

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.

I would think the same goes for the Erech stonet too. Numenoreans were probably just fond of black stone (probably obsidian), it seems.