This is my log of when I had gotten 600+ rarity (8/8) on a radiant fire moraine. I was using HQ level 55 gathering gear at the time (dhalmelskin, with only perception on perception pieces, and gathering on gathering pieces melded; no overmelds) with level 50 accessories (max melded dodore, etc.) and adamantite pick/sledgehammer (non-melded) sitting at around 598 gathering and 595 perception.
So yes, it's possible. Can you get it every time? probably not, it relies heavily on RNG.