Coincidence?

[Beanamir of Gondor]

Originally Posted by CSteefel

Yes, the basalt (which can contain glass, but typically includes annealed crystals) should be harder than obsidian, which is basically just a silica rich glass. As you say, shiny and develops a sharp point or edge, but not all that strong. Certainly it would chip. I always figured that Orthanc was something more like basalt, perhaps formerly the throat of a volcano (like the Devils Post Pile in Wyoming).

Like... Orodruin?
Ha. I had to say it. Perhaps the Numenoreans ventured into Mordor and dragged back some volcanic rock to build their tower in Isengard.