Does anyone know where the best place to mine it is?

I'd say crafting guild NW of rimmington.

Just find the closest place to the bank. If theres two rocks in a diagonal pattern, you don't need anymore. Even just one rock should repsawn fast enough.

If you have done quests to get in, just south of Pictoris colony... (prob spelt it wrong, they need to put spell check on here)...

in crafting guild, you can mine it, and craft it in less time, just bring a few buckets, and then fill them in sink, make soft clay, spin in clay spinner (duno what it is called) and then heat in pottery oven. very quick and nice experience

If you are banking it, use the mine just northeast of Yanille. I think it's one of the closest, of not The closest to a bank.