I found a fast way to get stone or clay!
All you need to do is:
1. Garb a pickaxe.
2. Equip it. (like you would do with a sword)
3. Head towards the stone/clay.
4. Keep attacking the stone by swinging the pickaxe on it. (If you have the daul weild perk this can be even faster!)

I found this saves alot of time by using this method.
Hope this helps!