Made on a carpentry shop from a Heavy mallet head, a large crude handle (requires Carving 3 and a Quality 3 knife), and a wooden peg (requires Carving 2 and a Quality 2 knife).
A Heavy Mallet is used for limestone gathering, and increases the yield to 3 per pull. (Soda gathering is unchanged at 1 deben about every 5 attempts. Confirmed at 1:14 ratio soda:limestone - Arpallan)
Heavy Mallets are best used in conjunction with a lead chisel. A Heavy Mallet will shatter a flint chisel, yielding 1 limestone as the chisel breaks.
Note: This should not be confused with a Lead Mallet, which has other uses (used to tap bore rods in Tale 2).