The Lost Mine of Phandelver adventure introduces Gundren Rockseeker simply as a "dwarf" and doesn't seem to mention what kind of dwarf he is. I've also tried to look for information about his brothers and it describes each those as simply being a "dwarf" as well.
So, in the Lost Mine of Phandelver text, are they ever referred to as Mountain Dwarves or Hill Dwarves?
It's just occurred to me that the name "Rockseeker" might be an established dwarf surname in Forgotten Realms lore, which I'm not all that familiar with, so if someone can provide an official reference to any information on the Rockseekers being Mountain Dwarves or Hill Dwarves, even if it's from other editions of D&D, then that would also be an acceptable answer, but I'd still prefer it if the answer came from the Lost Mine of Phandelver.
The reason is because I'm setting this in my home universe rather than the Forgotten Realms. The different dwarves have different accents. Mountain Dwarves have the stereotypical Scottish accent, but Hill Dwarves in my universe have northern accents (that is to say, North of England, specifically Geordie or Yorkshire accents), so this will affect how I play Gundren (since I like to try and do the voices for my characters if I can).
If it turns out that the adventure simply never states what kind of dwarves they are, then I'll simply pick one, but I'd prefer if I play them as the correct kind of dwarves if it does say which kind they are...