"Scheelite"
This author really has middle-schooler syndrome. I can picture them typing into google "what has the highest melting point", finding tungsten, then looking into the wikipedia article to find its chemical composition to look "cool" and "smart". Like they did with the fake blood earlier using the components of cinnabar, mercury and sulfur, instead of what actually makes blood red, iron oxide. Or making a net out of asbestos to catch the dragon.
It's like a kid making their DnD character yield a sword made of moissanite, because diamond is the hardest material in the world, but it's to "mainstream" so they picked the next best thing that nobody's heard of, while totally oblivious that their blade would shatter at the first impact.