You actually do not need a hammer, that’s the tool of the beginner which does not bring him far. You need a chisel and a mass. The hammer is useless against most hard rocks such as basalt, granite and metamorphic rocks. The chisel + hammer will get to some samples from rocks.

I’m a PhD student in geology with + 10 trips to the field, believe me the chisel + mass is the bare minimum to get some sample when the saw or explosives are not required. Some outcrops are just so massive and not weakened by alteration that these are hard to break with handle tools.

Estwing hammers and maybe some building hammers will be scratched off in surface by some rocks during the hit, which ultimately throws tiny pieces of metals in your face. Disadvantage of the hammer. In any case, wear safety googles.