A geologist's hammer, rock hammer, rock pick or geological pick is a hammer used for splitting and breaking rocks. In field geology, they are used to obtain a fresh surface of a rock in order to determine its composition, nature, mineralogy, history and field estimate of rock strength. In fossil collecting and mineral collecting, they are employed to break rocks with the aim of revealing fossils inside. Geologist's hammers are also sometimes used for scale in a photograph.
Geologist's hammers, as with most hammers, have two heads, one on either side. Most commonly the tool consists of a combination of a flat head, with either a chisel or a pick head at the other end.
- A chisel head (pictured), which is shaped like a chisel, is useful for clearing covering vegetation from exposures and is sometimes (though inadvisedly) used to pry open fissures. Some rocks can be easily split, like slate or shale, to reveal any fossils.
- A pick head, which terminates in a sharp point to deliver maximum pressure, is often preferred for harder rocks. A geologist's hammer bearing a pick end is often referred to as a rock pick or geological pick instead of a geologist's hammer.
- A flat head is used to deliver a blow to a rock with the intention of splitting it. Specimens or samples can be trimmed to remove sharp corners or reduce in size.
The effective power of a geologist's hammer is mainly considered to be a reflection of its head weight and handle length. Head weight may range from 8 oz (225 g) or less on a small hammer—such as would generally be used for casual use or by children—to 24 oz (680 g) and greater. 16 oz (450 g) is often quoted as sufficient for all rock types, although metamorphic or igneous rocks often require heavier hammers for a more powerful blow.
The best geologist's hammers are forged from one piece of hardened steel, which renders them sturdy and long lasting. Alternatives such as tubular and wooden shafted hammers are more commonly used, in part due to their low cost. Such alternative handles sacrifice strength and make the hammer unsuitable for high strain activities like prying.
The form and weighting of the shaft defines the balance, which itself defines the ease, efficiency and comfort of use of the geologist's hammer.