Collecting rocks and minerals

Collecting rocks and minerals is a fascinating hobby and one that teaches us a great deal about the Universe around us and the planet that we live on. Since earliest times man has used rock — first when he sheltered in caves, then when he used stones to carve weapons and tools. Even today, with all the technical expertise of our age, we still derive our basic materials from rocks. There is hardly an industry that does not depend directly or indirectly on the earth's crust. The houses we live in, the gas we cook on, the planes we fly in and the petrol they use are just a few of the products which have their bases in rocks and the minerals of which they are made up.

Our knowledge of rocks is still confined to those which have cooled down to form the earth's crust. Any given rock may be formed of one or several minerals. Some are hard; some are soft and powdery like sand or malleable like clay. The study of the earth's crust is such a complex subject that each aspect of it has its own specialists. Geologists study rock formations to determine how and when they were formed; petrographers identify and classify the rocks themselves, and mineralogists identify and study the minerals of which the rocks are composed.

To go into any of these aspects in any technical detail is well beyond the scope of this book; we want merely to introduce you to what can be a fascinating pastime and one from which you will learn a great deal.

Rocks in Britain
The British Isles are composed of an enormous variety of rocks which differ with the geographical area. It's taken some 3,000 million years to form them. On high ground you see them clearly as crags and cliffs; in lowlands they are exposed by excavation, (effected either by man or by nature,) in mines and quarries, cuttings and cliffs, by the sea or along a river.

Much rock in Britain has been covered by layers of clay or gravel left by the ice sheets of the Ice Age. The sand and gravel in river valleys is not as old. Below these surface materials are the sedimentary rocks laid down in ancient deltas or sea beds. They include limestone, clay and slate, often with fossils of plants and animals embedded in them. Volcanic rocks were formed when molten rock rose through the crust of the earth and poured out as lava or solidified in fissures in the crust. Metamorphic rocks are rocks which have been changed by the effects of heat and pressure.

The oldest rock formations in Britain are found in North-West Scotland, the most recently formed in South-East England. Britain divides into five regions:

In the South-East you will find limestone in the higher parts of the Cotswold; the chalk, a pure limestone which forms the Downs from Dorset to the Chilterns and the Yorkshire Wolds, while sand and clay cover East Anglia, Hampshire and the London area.

Wales and the West of England are rich in metamorphic rocks. There are various forms of granite in Devon and Cornwall, and old red sandstone in much of South East Wales and Hereford.

The Midlands, the Lake District and South Scotland are composed largely of sediments and volcanic rocks about 500 million years old.

The Scottish Highlands yield granite (Aberdeen is known as the Granite City), marble, slate, quartzite and mica; garnet crystals come from the northern Highlands.

From Ireland comes Con-nemara marble, Cork red marble and Merlin Park marble from Galway; copper pyrites from County Wick-low and beryl from County Donegal.

Crystals form a study of their own beyond the scope of this article. Sometimes they develop in clusters, or as twins. The study of how they are formed reveals mathematical relationships as amazing as the crystals themselves. Perfect crystals are rare, and some are of great value.

The amateur mineralogist
Collecting rocks and minerals is the first step towards learning about them. It is an activity which will take you out in the open and does not need good weather, so you can pursue it at any time of the year.

Where there are rocks you will find minerals. The most interesting deposits will be found where rocks have been laid bare by man or nature — steep river banks, cliffs, gravel pits, tunnels, quarries etc.

In quarries and mines always ask permission before you remove any specimen or you may start a landslide.

A good way to learn to distinguish the various types of minerals and rocks is to visit a museum. Many rocks and crystals can be bought from the Geological Museum shop, London SW7.

Looking for rocks means trudging over rough terrain, so equip yourself with strong boots with non-slip soles, thick trousers and tops to protect yourself from grazes, and a helmet such as builders wear in case of rock falls. You will need thick gloves to protect your hands and plastic goggles (not glass which can shatter and hurt your eyes) to protect you from flying chips of stone. Your equipment must include a geologist's hammer and a cold chisel to cut out the pieces of rock you want, a magnifying glass, and newspaper in which to wrap up your finds. Take along a strong but lightweight field bag in which to pack the rocks. Don't try and carry too much at a time, rocks are heavy things.

Take along a notebook and pencil to note what you found where. The size of your specimens is important. For convenience choose specimens the size of your fist and keep them all roughly to that size. But if you are lucky enough to possess a little microscope then your specimens can be as small as a thimble and will be that much easier to store.

From the start, have a card index system going, so that you know at a glance what you have collected. For each mineral write down the name and which group it belongs to as well as the place of origin. Density, hardness and the system of crystal formation should also be noted.

How you divide your collection is of course up to you. You can grade specimens according to topography, in other words which part of the country they come from, or to types. Whichever system of classification you use we suggest that you begin by numbering each specimen in Indian ink on a small patch of quick-drying enamel paint. The number will refer to entries in your card index, so that you know at a glance what is what.

A simple system of cataloguing your collection is to divide it into igneous, deposit and metamorphic rock and then further sub-divide each specimen according to its chemical composition. A second group could include all crystals and precious and semi-precious stones such as amethysts, agates, tourmalines and garnets. A third section could cover historical curiosities, such as petrified wood and plant and animal fossils, corals, arrowheads etc.

If all this has awakened your enthusiasm then turn to the many books written on the subject. And before you try to process your finds, that is remove the rock around the mineral, make sure that you know what you are doing or you may damage a good specimen.

For this job you will need a work bench, some hammers and chisels, a vice and grindstone, brushes, bradawls, and plastic containers in which to wash the minerals to remove with thinned acids the chalk impurities. Collectors sometimes polish their finds with wax to make them shine, or protect them from dust with a coating of colorless lacquer.