Collecting Geological Samples

The collection and curation of geological materials is a vital practice for researchers in understanding Earth's history and composition. Geological materials encompass a wide range of rock, mineral, and fossil specimens that hold clues to past geological events, climates, and life forms.

The first step involves collecting geological materials from the field. Geologists typically follow a meticulous process to ensure they gather valuable specimens while adhering to ethical and legal considerations. 

Collecting Geological Samples

Why collect?

So do you really need to collect?

What to Collect?

A general collection or a specialist one?

Most people start off collecting everything they find, but there comes a stage when you realise that you will not have enough space to collect everything! At this stage you should carefully consider your motivation and particular interests. Are you collecting to be able to have nice examples of all sorts of rocks, minerals and fossils, like the ones you can see in a museum? Or is there one or more aspect of geology that really excites you? If so it might make sense to specialise at an early stage, collecting a group of minerals or fossils, or specialising in a geographical area or geological timespan.

You may even end up just collecting from one bed of rock from one locality. There are scientific advantages in specialising it enables you to pick out the unusual, and perhaps make important discoveries. The disadvantage is that you have to take the 'bad' specimens with the 'good', because often the rare and unusual specimens are not display quality! But you may not be so limited if you go for something small you could study microfossils or go for micromount minerals.

When you are in the field always keep in mind your collecting policy and the reasons behind it. Don't collect just for the sake of it, always try to collect loose specimens for preference and if you must hammer at the rock face to collect a sample or specimen always ask yourself the following questions:

• Can I collect it safely, without risk to myself and others?
• Does it fit in with my collecting policy?
• Will it enhance my collection or research?
• Can I remove it without damaging it?
• Have I got enough room to store it?
• By removing it am I saving it from destruction by the elements?
• Is it still possible to study and interpret the outcrop without this specimen?
• Can I remove it without disfiguring the outcrop?

If the answer to any of these questions is no, then you should really not collect that specimen. Try looking for another, in a less prominent position, that is in softer rock and easier to collect.

Extract from Position Statement by English Nature on fossil collecting - " ... in general collect only a few specimens and obtain these from fallen or loose material. Detailed scientific study will require collection of fossils in situ. ....always record precisely the locality at which fossils are found and if collected in situ the relevant horizon details. Ensure that these records can be directly related to the specimens concerned. .... Fossils of key scientific importance should be placed in a suitable repository, normally a museum with adequate curatorial and storage facilities." (revised December 2000)

Labeling and Record Keeping.

The most important thing about a specimen is the information that comes with it. The name of a fossil or mineral may change as science advances but the information about where it came from will never change. A specimen without that information is just another pretty stone; it is not scientifically useful! So it is important to keep detailed information about your collection. 

Make notes in the field when you collect specimens, trying to record which part of the exposure and what level it comes from. (click here for suggestions about taking notes.) Label the specimen carefully. When you return home, number the specimen as part of your collection, enter details in you card index and/or logbook, and also put the details in the specimen tray. This is a real belt and braces job! And as I was saying to what's his name the other day "do not rely on your memory! "

It is best to label the specimens in a permanent way, by writing the catalogue number directly onto the specimen or on a white patch of paint on the specimen or on a label strongly glued to the specimen. If the specimen is small put a numbered label into its container or write on the mount. Do not just rely on the specimen's card being stored with the specimen! Remember to use indelible and light stable ink, I have not found anything to beat old-fashioned Indian Ink. Usually you can put the number on the back of the specimen, or on part which is less 'perfect' so that it does not detract from the appearance. It is worth adopting the museum practice of colour coding significant specimens, e.g. a red dot for a cited specimen and a green dot for a type specimen.

Storage and Conservation of Specimens

Conservation

There is a general rule in conservation that you should not do anything to a specimen which is irreversible! So always try to use materials that can be removed or cleaned off later. Always make a note in your records of what you have done to a specimen in case you should want to reverse the treatment later! When you collect the specimen in the field, wrap it up carefully and label it, so it does not get damaged on the journey home.

Try to trim it down to a manageable size in the field, but do not try to do too much work on it, it is easier at home when you have more time and better tools. When you get it home you will probably need to clean it, with the exception of some special cases listed below this can be done by washing in water, perhaps with the use of an old toothbrush.

You may have to 'prepare' the specimen also. This means that you are removing some of the rock matrix to expose more of the crystal or fossil, and also trim it to a more manageable size for your collection. Always prepare the specimen with care, you do not want to damage it. This is an art that you will have to learn with experience, so it is a good idea to practice on pieces of rock which you have to spare. You can use a light hammer and fine chisel, I find that masonry nails are good for fine scale work. Or you can use a small drill, vibrotool or 'airbrasive'. Always wear safety goggles or glasses when hammering rocks!

When you collect specimens, often they will be damaged or broken. Occasionally they will break when you handle them. They will need to be repaired. Once again it is important to note any repair work you do, so that it can be reversed later if needs be. As a general rule always use a process that can be reversed later and always use a glue that is less strong than the rock so that if it breaks again it breaks in the same place and not a new one!

Although we might want to have perfect display specimens, it is not always a good idea to use filler to recreate the bits that are missing, it might make the thing look nicer but it is creating your impression of how it should look and not the real thing. Always ask yourself whether you really need to repair a broken specimen; often the break will allow you to see some of the internal structure, and study it. Broken specimens are often more scientifically useful than repaired, reconstructed, 'perfect' display specimens.

Special Problems

Pyrite: Pyrite and the presence of pyrite in specimens causes real problems. This iron sulfide oxidises in damp conditions to leave sulfuric acid and a white powder. So suddenly, after a period of a few years, you open a drawer to find that your favourite fossil is now a pile of white crystals and there is a large burn mark beneath it! There seems to be a bigger problem with pyrite fossils than it is with pyrite in igneous and metamorphic rocks.

Specimens found on the coast seem to be more prone to rot perhaps because of the presence of sea salt. Firstly it tarnishes quite rapidly, so the shiny golden specimens you collect are dull a week later unless you protect them fast! The same is also true of other sulfide minerals. If you can control the humidity then your specimens could well survive for ever. But for most of us this is not practical so we should look to provide a damp free microenvironment for them.

Small specimens can be kept in sealed tubes, and/or stored under oil. Larger specimens could be coated with varnish, wax or PVA; some people swear by antiseptic ointment believing that the rot is caused by bacteria, though the oils in ointment could be keeping out the damp. Or they could be kept in sealed bags or containers, perhaps with a sachet of silica gel desiccant. If your local museum has the right humidity controlled conditions it may be best in the long term for you to donate the larger specimens for them to take care of.

Salt in specimens: When you collect rocks and fossils from the coast porous or semi porous specimens will be impregnated with sea salt. When they slowly dry out in the dryer conditions of your home the salt will crystallise. The surface of the rock may flake off or the complete specimen may crack and fall apart. It has happened to some of my best chalk fossils: suddenly there is a pile of white chalk dust where they once stood! If you cannot control the humidity (and in this case keep them damp!) you should try your best to remove the salt, by continued soakings in fresh water, over a period of months! One chalk researcher I know leaves them in his toilet cistern so that the water is changed ever time he flushes the loo! Alternatively you can try adding glue to strengthen the fossil. I have used dilute PVA emulsion with some success, but if it does not work then damage to the specimen is even more dramatic!

Fossil plants: These are either solid structures, replaced by sediment or minerals, or a carbon film. Be very careful when cleaning these, scrubbing a carbonised leaf with a strong brush under water will rub it away! Ideally you should leave these leaves untreated, but they can peel off the rock if you do. A friend of mine used to put varnish over them, to preserve them and enhance their appearance. One textbook recommends using the aerosol spray that artists use to stabilise pencil and charcoal drawings. If you plan ahead this could be applied in the field.

Solid pieces of fossil wood can crack when they dry out. Fossil wood is often associated with pyrite, which can rot (see above).

Sub Fossil Bone: Specimens such as teeth, tusk and bone from the Pleistocene are prone to cracking if they are stored in humid conditions. You can try varnishing them; some workers favour Shellac, but mammoth tusks I have seen which have been varnished have also cracked and peeled. The best thing you can do to conserve them is to give them to a museum where they can be stored in the right conditions.

Hygroscopic Specimens: Some minerals, such a halite, absorb water and eventually start to dissolve. Once again they require storage in low humidity or sealing away from the damp. They can be varnished, sealed in wax, stored under oil or stored in an airtight container.

Clays and fossils in clays and silts: Clay minerals have very small crystals, about 0.002mm in size, and are often poorly cemented when in soft rocks. So do not try to clean fossils preserved in clay, or impressions in clay, as they will wash away! On the other hand when you have hard fossils or nodules in clay then you can clean them very easily by gently scrubbing under water, and they are often very well preserved. Another feature of clay minerals is that they swell when damp. So when you collect clay samples/fossils which are damp they will often crack when they dry out, and are particularly difficult to glue back together. The best thing you can do is wrap them well in a lot of newspaper and allow then to dry very slowly, even then you can expect a 50% (or higher) failure rate. If it is still fragile you could try consolidating it with dilute PVA.

Specialised collections

A geological collection can take up a lot of space! But you could consider collecting smaller specimens. There are other advantages too small crystals and fossils are more common and also more often complete and perfectly formed. There is a disadvantage though you may need to invest in specialist equipment: microscopes, sieves, rock cutting saws, tumblers etc.

Polished rocks. When you collect rocks from the beach they often look impressive and shiny, because they are wet! When you get them home they and the rocks have dried you will often wonder why you collected them! One thing you can do to re capture the details of the rock is to polish the rock. You can tumble it in a tumbler or grind a flat surface and polish it. Try asking your local lapidary society for advice and help.

Thin Sections. These are thin slices of rock, ground to 0.030mm thick, which are almost transparent when viewed under a microscope. Using a polarising microscope you can study the optical properties of the minerals in the rock.

Acetate peels. Thin sheets of acetate pressed on to a polished, slightly etched, rock will pick up the fine detail and can then be studied with a microscope or hand lens.

Micromount minerals. Small crystals or clusters of crystals mounted and studied under a binocular microscope.

Microfossils. Small fossils which can be extracted from soft sediments and viewed under a binocular microscope. Foraminifera and Ostracods are very common in most soft sediments. Meso-fossils can be studied using a hand lens such things as crinoid ossicles, fish teeth, echinoid spines or plates and starfish; until you look for them you do not realise how common they are.

Nanofossils. Very small fossils, requiring the use of a high power microscope and specialised techniques to extract them from the rock. Probably outside the scope of the amateur.

Identification