Fossil collecting



Fossil collecting describes the extraction of fossilised material for profit, pleasure, or scientific study. Fossils - the preserved remains of long-dead organisms - are found in many places where sedimentary rocks, such as claystones, shales, limestones, and sandstones, are exposed. Only certain sedimentary rocks harboured the appropriate environmental conditions to preserve and yield fossils, which are often concentrated along particular bedding planes within the rocks.

Finding fossils
Fossils are generally found in sedimentary rock with differentiated strata representing a succession of deposited material.

The occurrence of fossil bearing material depends on environmental factors before and after the time of preservation. After death, the first preserving factor is a rapid burial in water bodies or terrestrial sediment which would help in preserving the specimen. These rocks types are usually termed clastic rock, and are further subdivided into fine, medium and coarse grained material. While fossil's can be found in all grain typed, more detailed specimens are found in the fine grained material. A second type of burial is the non-clastic rock, form where the rock is made up of the precipitation of compacted fossil material, types of rock include limestone and coal. The third fossil bearing material is the evaporates, which precipitate out of concentrated dissolved salts to form nodular deposits, examples include rock salt and phosphate concentrations. The evaporates are usually associated with gastropod, algae, vertebrate, and trace fossils. After burial various factors are at work to endanger the current fossil's preserved state. Chemical alteration would change the mineral composition of the fossil, but generally not its appearance, lithification would distort its appearance, the fossil itself may be fully or partially dissolved leaving only a fossil mold.

Areas where sedimentary rocks are being eroded include exposed Mountainous areas, river banks and beds and engineering features like quarries and road cuts. Generally in appearance, a fossil will be either a different colour to the surrounding rock, because of the different mineral content, will have a defining shape and texture or a combination of both. Dried up natural lake beads and caves in the form of pitfall traps also has an occurrence of a recent fossil fauna for the locality as is the case with Cuddie Springs and Naracoorte Caves in Australia.

Fossils are not to be found in areas of igneous rock (except in some beds between lava flows). In rocks which have undergone metamorphism, they are usually so distorted that they are difficult to recognize or have been destroyed completely.

Artificial exposures, such as road cuttings or quarries, can often be good collecting spots, along with continually eroding river or coastal exposures. Coal mining operations often yield excellent fossil plants, but the best ones are to be found not in the coal itself but in the associated sedimentary rock deposits called coal measures.

In hilly regions the best sections are often those exposed at the sides of streams that have cut into the bedrock.

Wave washed sea cliffs and foreshore exposures are often good places to search for fossils, but always be aware of the state of the tides in the area. Never take chances by climbing high cliffs of crumbling rock or clay (many have died attempting it).

Exposures of softer rocks, such as clays and sands, can be good collecting spots. However inland sections tend to degrade rapidly, becoming overgrown, and are lost forever.

Collecting ethics
To collect fossils, there are various legal realties that must be observed. Permission should be sought before collection begins on private land.

Hammering the rocks in national parks and other areas of natural beauty is often discouraged and in most cases is illegal.

Equipment
It is important to have the right kind of field equipment when looking for fossils, and safety should always be an important concern.

A hard hat is essential protection from loose stones that may be dislodged from cliffs above, but will not protect the wearer from larger falling rocks. Hard hats are normally a requirement in operational quarries.

Safety goggles and protective gloves are also essential, as rocks can be sharp and dangerous; safety goggles will protect eyes from chips produced while hammering, and gloves protect the hands.

A collector need dress appropriately for collecting trips, taking into account the climate and terrain of the area. Sturdy footwear, such as walking or hiking boots with steel toes, are recommended. A hammer, chisel and wrapping materials are the basic equipment required for fossil collecting, along with a stout rucksack or canvas bag for carrying equipment and fossil finds. The steel of many ordinary hammers is too soft for use on most type of rock. The steel may splinter, and the flying fragments cause injury to the person using the hammer, or others in the vicinity. The hammer should always strike away from the body. The head of a geological hammer or rock pick is made from specially hardened steel designed for use on rocks. The head is either firmly attached to a wooden shaft, or the hammer have the head and the shaft formed from one piece of steel. The head may have any combination of a square face, a tapered point, or a straight chisel edge. The point of such picks are not meant for striking rock directly, but for tapping rock (such as shale) open along planes and for prying: the hammer end is used for striking.

A convenient weight for a general purpose geological hammer or rock pick is around 1 kg (2 to 3 pounds). For breaking very hard rocks one may need a hammer of between 3 and 6.5 kg (7 and 14 pounds) in weight, with a correspondingly longer and thicker shaft. A hammer that is too heavy is tiring to use and results in unsafe work.

For extracting fossils from harder rocks, a sturdy mallet and cold steel chisels may also be required. Usually one needs a range of chisels in size from small ones with a sharp edge of about 1 cm (quarter of an inch), to much larger and heavier chisels. A broad-bladed chisel is often very useful for splitting rocks along their bedding plane.

Different types of rocks will break differently and a beginner should put in a little practice, getting the feel for a particular type of rock before he or she starts hammering out fossils. It is all too easy to ruin a specimen with one ill-placed blow of a hammer.

Extracting a specimen that is embedded in solid rock may prove to be a long and difficult process. Before attempting to extract a specimen, the collector should make sure that it is feasible to remove it without destroying or damaging it. Leaving sufficient rock beneath the specimen to protect it from fracturing; excess matrix can be trimmed at a later time.

For soft sediments and unconsolidated deposits, such as sands, silts and clays, a spade and a flat-bladed trowel or stout bladed knife may be the most useful tools for clearing the area around a fossil. Brushes are also useful for removing loose sediment from around fossils.

A sieve is used to separate fossils from sands and gravels. A smaller mesh is required in order to avoid losing small fossils. One practical difficulty with using sieves in the field is that they easily become clogged, especially when the material sieved has a high moisture content. However, under dry weather conditions the more durable fossils, such as teeth and bones, can be quickly and easily sieved out of loose sands. Shaking the sieve is always liable to damage or destroy fragile fossils.

If there is water available, such as on a beach or next to a stream, the material containing the fossils can be sieved wet and the matrix gradually washed away. Wet sieving is a technique that is frequently used for the collection of small mammalian fossils, and by using this technique even the smallest specimens may be recovered.

Preservation and documentation
A knowledge of the precise location a fossil was found greatly increases its scientific value. Details of the parent rock strata, the location of the find, and other fossil material associated with the find help scientists to place the fossil in context, in terms of the time, location and situation in which the organism lived.

Logging, photographing, and sketching may accompany detailed field notes to assist in the locating of a fossiliferous outcrop; individual fossils are ideally labeled with a locality number alongside their specimen number for later identification.

To avoid damage to fossils, collectors store them in a breathable bag, ideally made from a breathable fabric such as Tyvek, to avoid the growth of mold; suitable padding is also applied.

Occasionally, large fragile specimens may need to be surrounded and supported using a jacket of plaster before their removal from the rock: This protects the fossil, protecting it from shattering. If a fossil is to be left in situ, a cast may be produced, using plaster of paris or latex - whilst not preserving every detail, such a cast is inexpensive, easier to transport, causes less damage to the environment, and leaves the fossil in place for others to enjoy. Subtle fossils which are preserved solely as impressions in sandy layers, such as the Ediacaran fossils, are usually sampled by means of a cast, which shows up detail more clearly than the rock itself.