I’m guessing this is from a video game of some sort. Am I right? But, really, is it true. Must be. I mean if lava is basically molten earth, it stands to reason it’s hot enough to melt a diamond. Though, those diamonds have been through quite a chemical transformation, under a lot of pressure, to get where they are so who knows.
And just kidding about not knowing where this is from. Obviously, this is a Minecraft reference: