A geological hammer is necessary for most geological fieldwork, both for the collection of samples and, where necessary, to create fresh surfaces so that the rock and the minerals within it can be described (Figure 1). Having said this it is perfectly possible to do a lot of geological fieldwork without a hammer provided samples are not required. Rocks that are exposed in sea – cliffs and along foreshores, in new trenches or in road cuts often do not need hammering and indeed the slightly weathered or wave washed surface is often as good as, if not better than, a hammered surface. For sedimentary rocks a 1 lb ( c. 0.5 kg) hammer is often sufficient. For igneous, metamorphic and hard or well – cemented sedimentary rocks a 2 lb ( cca. 1 kg) or even a sledge – hammer may be necessary if good quality and/or large samples are required. However, a good chisel or pick hammer can be used to exploit planes of weakness (joints, bedding planes, foliation, vein margins) and extract samples from tougher rock types.
For safety reasons it is important to use a geological hammer rather than one designed for other materials such as wood or metal. This is because to hammer rocks you need a head that is robustly mounted on to the hammer shaft, made of a suitable grade of steel that will not splinter and is of an appropriate ergonomic design. Brick and stone hammers can be used if a specific geological hammer is not available. Other features to consider when purchasing a hammer are the type of head that is most suitable for your use and whether it feels comfortable when you use it. All geological hammers have one flat face: the other end is either a chisel or pick (Figure 1 ).
The chisel end is useful for splitting rocks apart although it is not as effective or accurate as using a hammer with a separate chisel; the pick is useful for hammering into crevices to lever samples out and for generally weakening a rock surface before extracting a sample. Some geological hammers have the head and shaft all cast from one piece of metal and this makes them exceedingly robust; however, they pass more of the impact from hammering through the shaft and into your hand and arm. The other option is a steel head mounted on a wooden or fibreglass shaft. The shaft on these absorbs most of the impact; however, the head on this type of hammer can work its way off. This is, however, very uncommon with the new fibreglass models. Note that the rust on the hammer or chisel that is an inevitable consequence of use in wet conditions (e.g. Figure 1 items 2, 4, and 5) is a potential contaminant for samples being used for geochemical analysis. The hammer can be cleaned with a wire brush and wire wool (e.g. Figure 1 , item 1). If the rocks have no good partings or fractures and/or precisely placed samples are required, it is best to use a chisel. Many of the larger cold chisels are now supplied with hand guards (Figure 1 , item 3). For delicate specimens such as fossils or minerals a small pencil chisel is useful (Figure 1 , item 6). If you need to do lots of chiselling, a lump or crack hammer may be useful (Figure 1 , item 8). For unconsolidated and poorly consolidated sedimentary deposits a spade or hoe pick and/or a masonry trowel is invaluable for removing the weathered or slipped material on the surface and then cleaning the surface so that the sedimentary structures can be seen ( Figure 2 a). If the surface of the rock is hard and coated with a thin layer of lichen, moss or iron minerals and there is not an alternative exposure surface, a hard nylon brush or a wire brush can be used to clean the surface.