A brief description of every geologist's most essential tool
Put simply, a geological hammer is a hammer used for breaking or examining rocks.
Hammers vary in two key respects: The head, and the forging.
The head's weight is an important consideration - 16oz is suitable for almost all everyday use but someone with an interest in metamorphic rocks, or minerals, may find a larger head useful. Of course many casual users will prefer something lighter, though these are increasingly hard to source.
Light hammers will suffice for most sediments - thus are handy for fossil hunters - but will be less effective when confronted with a granite or marble.
The shape of the head is another key difference. Essentially it is the blunt end that is the most used for hammering, the other end being primarily for picking or scraping at covering materials.
Thus those with a key interest in minerals are likely to favour a pick end - the head culminating in a point - whilst many favour the chisel end, which I find comes in handy when prying apart layers (although some say this is quite bad for the hammer and may shorten it's life).
The forging of the hammer is a mark of its durability.
The creme de la creme is a one-piece drop forged hammer, such as manufactured by Estwing. This is made of one piece of metal and thus cannot come to pieces!
A solid or tubular shaft hammer comprises a separate handle and head, joined together - this joint provides a point of weakness which may eventually fail. Most hammers should last for a long time before this becomes an issue, but as failure is often unpredictable it may cause a hazard or worry. A tubular shaft is hollow, and thus lighter; it also allows the hammer to be better weighted; a solid shaft is more durable.
A wooden shaft hammer has the shortest life, especially if extreme care is taken when hammering, since as the wood strikes rock, wear is caused and the handle decays. However, you can at least see when the time is coming to replace the implement.
The length of the handle is a consideration for some - extra long handles being available, allowing a more powerful blow, and greater distance to be maintained from the rock - protecting the user from shrapnel. However a short shaft is preferred by some for ease of carriage or handling.
The first thing to do is to chose what to hit.
It is always preferable to knock loose stones than bedrock, for many reasons - primarily, the preservation of the locality for future geologists; additionally, your finds will be easier to take away with you, and it is easier to manipulate or break the rock. The blow should be aimed along a plane of weakness, to split the rock - typically a 'bedding plane' (layer) in sedimentary rocks. Not only are such planes the most likely to display attractive fossils, but the rocks will break more easily into fewer pieces.
If one must hit an outcrop, loose corners should be the target - hitting a solid face will produce dangerous chips and sparks and won't reveal anything interesting.
The most interesting faces are those that aren't weathered. The outside of most rocks tends to be a different colour and consistency than its insides, due to the erosive action of wind, air and vegetation. Fissures are often affected in this fashion and can reach quite deep into a rock; when a block breaks easily in two, it may be along a weathering face - making it worth hitting the rocks further.
To avoid the danger of fragments of rock becoming embedded in the eyes, it's advisable to wear goggles at all times when hammering - especially when hitting harder rocks.
Other items of interest may be 'chert nodules' - lumps of flint that form around a central nucleus. Often this nucleus may be a fossil - though it may be something such as a lump of stone or a tunnel. In certain localities up to a quarter of these nodules may be fossil-bearing, but others are less productive.
Finding a suitable locality and where to hammer is one of the primary difficulties facing potential fossil hunters; local tourist information centres or mineral shops may be helpful, but remember that some parts of the world are better than others. Coastline is the main place where enough rocks are exposed to find fossils, but if it's the wrong type of rock then this may be no use.
Lyme Regis is Britain's 'fossil capital' - with many beautiful localities with spectacular fossils. much of the region is a protected SSSI (Site of Special Scientific Interest) and hunters should keep their eyes peeled for hammering restrictions - the useful book Fossil Hunting Around Lyme Regis tells you all you need to know.
A cheap and handy map of the Dorset coastline highlighting key fossil localities can be found here. I've not come across any for other areas but if you do have anything you could recommend, please do drop me an e-mail at MartinS [at] gmail,com.
The best deal I've seen on hammers is to be found at GeoLogic, a small specialist company which provides good quality geological hammers and excellent customer service, and at prices you'll find hard to beat.
You can also buy them in the real world at good builder's merchants, though you may be limited in choice, and they're generally more expensive than the internet.
Axminster Power Tool Centre are also a reputable and sensibly priced source of branded (Estwing) hammers.