This is the most typical rock hammer, also called a rock pick or prospector's pick. The hammer head is used for breaking and trimming small rocks as well as light chisel driving, and the sharp pick end is for light prying and grubbing in loose or weathered rock. It's a good compromise for a variety of uses. All rock hammers should be used wearing eye protection, because chips from rocks or from the hammer can fly in all directions. This hammer must not be treated as a chisel, being struck with another hammer, because the hardened steel head can send off chips. Chisels are made of a softer steel suitable for being hammered.
This hammer is not the well-known Estwing but one made by Vaughan that I bought at a large hardware store. It's the one I keep in the car most of the time.