agen_kolar
Super Freak
I didn't read the spoilers, but it's simply a statement of fact that obsidian glass makes for some of the the sharpest cutting edges possible. Obsidian fractures can be as narrow as one molecule. The Mayans used to make spears and battle clubs with it. Biggest drawback is it's brittle (like any glass).
It's also extremely dark and can be used in welding masks. I'm just guessing, but I imagine that might one day be useful against a dragon.
EDIT: If I had a piece of obsidian I'd be outside watching the solar eclipse.
That wasn't directed at you, just a general statement. I thought I saw some spoilers coming out and wanted to remind people that some of us don't know the story beyond what airs each Sunday night.
This episode wasn't as good as the previous ones, perhaps the weakest in the season thus far.