This is per Word of God. At a convention early after RWBYā'ās premiere Miles Luna, co-creator and -writer of RWBY as well as the voice actor for Jaune Arc, was asked, "What is Dust?" His one-word answer was "Mana". He subsequently elaborated on it, but right from the start, it was made clear that Dust is mineralized Mana. (A popular theory among folks I know who are RWBY fans is that Dust is the fossilized magic of Humanity V1.0.)
Topic on Trope Workshop talk:Exclusive Armaments
Well, that's news to me. I never knew that information like that could be gained from conventions.
You weren't aware that there have been scores of panels on RWBY at conventions over the past ten years -- in particular at Rooster Teeth's own annual convention, RTX? You can find dozens of panels and short clips from panels on YouTube with a simple search (see this playlist of 104 videos of panels or segments of panels), where the creators and/or the performers discuss the show. You can also learn a great deal from the commentary tracks on the DVDs.
Yeah, I'm a causal fan and I have only been to like two conventions so far. Thanks for the links on YouTube! I don't own any of the DVDs either.