Modern society is highly dependent on materials, usually referred to as minerals, whether in raw or refined form. All these materials have to be found, extracted and processed before use and disposed of afterwards. During their 'life cycle' they have a variety of impacts on the environment, ranging from the noise and dust arising from gravel extraction through to potentially lethal effects of toxic or radioactive metals.

The major source of all minerals is the rocks of the earth's crust. The minerals of the mantle and the core, however desirable they may be, are totally inaccessible for commercial purposes. Three aspects of minerals are relevant in relation to their use in building or industry: their overall abundance or rarity, the ways they may be locally concentrated and the ease or difficulty of obtaining useful materials, particularly pure elements, from their natural sources. The latter is bound to be a serious problem because earth minerals will mostly be in a chemically stable form and only a handful of elements, for example copper and gold, are stable in their pure forms. Because of this, finding usable deposits of many minerals has been called a geochemical lottery.

Although around ninety chemical elements occur naturally in the Earth's crust, they vary enormously in their abundance. Two elements are vastly more abundant than any others: oxygen (nearly 47 per cent) and silicon (nearly 28 per cent). Aluminium (eight per cent) and iron (five per cent) follow, then four light metals — calcium, sodium, potassium and magnesium (each two or three per cent). These eight elements make up almost 99 per cent of the crust, so all other elements are relatively rare. Indeed, some commonly used elements such as zinc, copper, nickel and lead occur as only a few dozen parts per million, tin and uranium at two parts per million and gold at four parts per trillion.

Three things are immediately apparent from this list. First, use of pure elements has little to do with their abundance - the oxygen in the air or the silicon used in chips are a minute fraction of the amounts which exist in chemical combination, while gold and uranium are eagerly sought after in spite of their rarity. Second, we unknowingly use most elements as chemical combinations - sand being the familiar form of silica (silicon oxide) and many rocks being complex 'aluminosilicates'. Third, even where elements are used in their pure form, the amounts used depend on how they are concentrated by natural processes and how easily they are purified chemically.

Most of the earth's crust is made up of igneous rocks (those which have solidified from a molten state), which all contain aluminosilicates of the abundant metals. Some of them, acid or granitic rocks, contain at least 50 per cent silica. These rocks are chemically rather stable, so even though they contain vast quantities of iron and aluminium they are not used as ores but only as rocks, for building or in crushed form for aggregate, road beds and so on. Workable ores result from natural concentrations of minerals which are more amenable to chemical purification.

Iron is the fourth most abundant element in the crust and is concentrated in three ways. The highest grade ores, with more than 60 per cent iron, are 'magnetites', for example from Sweden, and 'haematites', such as those formerly mined in Cumbria. Though restricted in size, they are very pure and make up one third of world reserves. The most important sources of iron, half today's total, are the 'banded ironstones' from the oldest parts of the continents. The deposits are hundreds of metres thick and some extend hundreds of kilometres. They are much less pure and have to be milled, separated from the silica component and made into pellets for smelting; so they came into use later than other types of ore. The more recent sedimentary ores are low grade but were important in the early growth of industrialisation in Europe and North America. They are going out of use now that bulk carriers can move higher grade ores halfway across the world. Blast furnaces and steelworks can be run at any port site where efficient production and local demand make it profitable to do so. It also means that pollution from smelters is more likely to be found in industrial areas than at the source of the ore.

It is apparent that about half of the metals required have over one-third of world production coming from a single country. What is not apparent from this figure is the domination of production and trade by transnational companies. Just as the oil industry is dominated by seven corporations, so six dominate aluminium trade, two dominate nickel and three uranium. Past attempts by governments of less developed countries such as Zaire, Zambia and Peru to expropriate or tax mining operations run by transnational have led to a concentration of exploration into politically 'safe' countries. In fact 80 per cent of 'free world' exploration effort is expended in the USA, Canada, Australia and South Africa and very little now occurs in less developed countries.

Some of these metals, notably aluminium, manganese, magnesium, chrome and titanium, are geologically abundant so, in spite of substantial and growing production, there are few problems of supply. The other metals are scarcer, which leads at best to the use of lean ores - down to half per cent for copper ores - and at worst to actual and potential shortages, as with silver, tungsten and tin. The results for the environment are damaging - large voids and spoil heaps, use of large amounts of energy in extraction and pressure to exploit existing deposits to the maximum.

The main environmental impact issues are concerned with the environmental effects of mining and the processing of minerals, and with policies for the rehabilitation of dam aged land scapes and the control of associated pollution.

A classic case of substitution is in electrical uses of copper. Early this century copper was used for all electrical wiring including transatlantic cables. Since then the relative scarcity and consequent high price of copper have led to substitution. Aluminium was a suitable substitute in cables, but the demand for metal cables has been reduced by the use of optical-fibre cables over short distances, microwave transmitters at medium scale and satellites over the longer distances. These substitutes use fewer, cheaper or more abundant minerals but have one major problem. Although more efficient in use of materials, they are more energy intensive and hence put pressure on two of the minerals in finite supply: coal and petroleum. Similar problems arise from the substitution of plastics (which are mostly made from oil) for metal. A more promising strategy for the future is to use more ceramics, since clay is abundantly available.

Recycling looks an even more promising strategy since re-use of materials can simultaneously solve problems of mining, refining and disposal. At best, for example in the case of the re-use of aluminium or glass, it is also much less energy intensive. Indeed, recycling is so obviously advantageous that it is surprising that only between one- quarter and one-third of metals output uses recycled materials. At present, the problem lies in the great complexity of products like cars. Not only do they involve metals other than steel, but they include many different kinds of steel. A recycled batch of steel may contain appreciable quantities of chromium, cobalt, manganese, nickel, tungsten and/or vanadium. These become impurities which make its behaviour unpredictable and at present no practical technology exists to remove them. As a result, scrap has to be combined with new steel and confined to low grade uses. Similar problems arise with aluminium: recycled aluminium is insufficiently pure to use for wire or sheet. Unfortunately, demand for cast aluminium is not high at present. No doubt these kinds of problems could be resolved but at present the financial incentives are not strong enough to persuade industry to make the necessary commitments to new technology and more expensive processes.