It's possible to farm infinite moonrock nuggets with the moon altar ("moonbase").
The altar requires 1 moonrock to repair to the first stage and has a chance to drop 2 moonrocks when destroyed at any stage
Destroy it via gunpowder, slime, ground pounds, giant collision, etc.
Repeat infinite times.
-Shatter it with various methods
-Do one repair (1 moonrock)
-Shatter it again and collect 2 moonrock (drop chance is either 1 or 2 rocks so it might take a few additional attempts)