nice job loving ignoring my edit.
You play too much minecraft.Obsidian is quite a fragile material. It can be sharpened down quite easily, and is nowhere near as strong as diamond. It's actually about has fragile as glass. Considering it IS glass.
Obsidian is almost as sharp as diamond, though. And diamond itself is fairly brittle.
Not to shatter it. To cut it, yes. But not to break it.