From the bowels of the earth: ores and dignified metals

Copper was the first metal that man discovered in the earth’s crust. It could be formed into simple tools or weapons and was so important that an entire era was named after it: the Copper Age. The tools got better when man mixed the copper with tin and thus invented bronze. And when he learned to smelt iron, the triumph of metal tools finally began.

Unlike the Earth’s core, the Earth’s crust consists largely of non-metals. Nevertheless, metals such as iron, aluminium, manganese or potassium can be found in its rock. Experts (geochemists) can determine exactly how often they occur. They have found out, for example, that about seven per cent of the earth’s crust consists of iron.

Like most metals, iron occurs as a chemical compound with other elements, as so-called ore. To extract iron from ore rock, the ore rock is ground, mixed with coal and heated. A chemical reaction then takes place that removes the other elements from the ore, leaving the pure, elemental iron.

Some metals, on the other hand, hardly combine with other elements. They therefore do not weather and occur in the earth’s crust in pure form. These “solid metals” include gold, silver or platinum. Platinum and gold are also extremely rare: On average, only 0.001 grams of gold is contained in one tonne of rock. However, a place is only called a deposit when it contains a thousand times the amount of gold – i.e. one gram of gold per tonne of rock.

More common than gold or platinum are the “rare earth metals”. What sounds strange has a simple reason: These metals are considered rare because they do not form their own deposits, i.e. they do not occur in concentrations but only in scattered form. This is why we also talk about spice metals. Their importance has increased greatly in recent years because they are needed for the production of electronic devices such as mobile phones or computers.

California’s Gold Rush

It happened on 24 January last year in a sawmill on the American River: During construction work on a sawmill, James Wilson Marshall discovered a gold nugget. Although attempts were made to keep the find a secret, word spread quickly: there is gold on the American River!

Soon the first gold prospectors from all over California crowded to the river. Thousands of workers in San Francisco threw down their jobs and came to make their fortune on the riverbank. But it was not only the inhabitants of the country who were gripped by gold fever. More than 50,000 people from Mexico, Chile, China and above all Europe flocked to California and flooded the cities here. San Francisco in particular was bursting at the seams by the migration. In just one year since the discovery of the first gold nugget, the Californian population has now grown fivefold.

The hopes of the immigrants are high, the yield from gold panning often low. Although, with a bit of luck, much more can be earned here than a worker receives as wages on the East Coast, life in the gold-mining sites is expensive. Simple foodstuffs have to be bought at exorbitant prices. An egg costs a dollar, a newspaper even ten! On top of that, some prospectors blow their new wealth on gambling or alcohol in the saloons. For some, the gold rush has already ended with a nasty hangover.

Washing gold – how does it work?

The technique of the Californian gold prospectors is simple: the search does not require much more than a tin pan and a leather bag. You shovel sand and silt from the river into the pan. When you swirl the pan, water and sand are flushed to the edge. Now it gets exciting: with a lot of luck, small pieces of gold flash at the bottom of the pan. Because they are heavier than the rest, they remain in the middle. The gold pieces can be collected in a leather bag and the next pan is next. Good luck!

Gemstones

Whether green emerald, blue sapphire or red ruby: we know gemstones as sparkling and particularly valuable pieces of jewellery. Yet gemstones are simply minerals. However, they have to fulfil three conditions to be considered precious stones: They must be particularly rare, transparent and at the same time very hard.

Gemstones are formed deep inside the earth under high pressure and at high temperatures. The hardest among them and at the same time the hardest known mineral is the diamond. It forms at a depth of about 150 kilometres at temperatures of over 1200 degrees Celsius from a single element: carbon. In the process, crystals develop from mostly eight equilateral triangles, called octahedrons. Other shapes such as cubes are also possible. The diamond comes to the earth’s surface by being thrown upwards together with rising magma. The largest diamond ever found is the so-called “Cullinan”. It was discovered in 1905 in a South African mine and weighed exactly 3106.75 carats in its rough state. This corresponds to a weight of 621.35 grams.

Whether diamond, amethyst, emerald or topaz – all gemstones differ from each other in structure, composition and colour. They all only become particularly beautiful and shiny through the cut. It makes the colours of the gemstones really shine through a certain refraction of light.

In addition to gemstones, other gemstones such as blue lapis lazuli or green malachite are found in the earth’s crust. While these are also highly sought after and beautiful, they are not transparent and are too common to be considered gemstones.

Treasures at the bottom of the sea

Deep down at the bottom of the ocean lie hidden treasures. We are not talking about the sunken booty of predatory seafarers here; we are talking about raw materials found on the ocean floor.

One of these raw materials is methane hydrate. This combustible ice is stored on the seabed at a depth of more than 500 metres. It has formed at low temperature and under high pressure from water and methane, which is produced by certain single-celled organisms during metabolism. The estimated deposits of methane hydrate contain over twice as much carbon as all the oil, natural gas and coal reserves on earth. Whether it can contribute to our energy supply in the future, however, is controversial. It is difficult to extract because it decomposes easily at higher temperatures, releasing methane. The danger here is that methane is a greenhouse gas. If too much of it enters the atmosphere, it will affect our climate and temperatures will rise.

At a depth of about 5,000 metres, there is another strange substance at the bottom of the Pacific Ocean: manganese nodules. These black lumps can grow to the size of potatoes, some even to the size of heads of lettuce. They are interesting to humans as a raw material because they contain large amounts of the metals manganese and iron. But the wrinkled structures also contain high amounts of copper, nickel and cobalt – metals that are needed in the electrical industry and for steel production. Whether their extraction is worthwhile still needs to be researched: Although they have a much higher metal concentration than ore mines on land, the mining of manganese nodules is particularly complicated because of the great ocean depth at which they occur.

Fossil fuels: oil, natural gas and coal

It is called black gold because of its colour and because it is so valuable to us: we are talking about crude oil. The raw material was created 150 million years ago when dinosaurs still inhabited our planet. Today, it is hard to imagine our everyday life without petroleum: we need it as fuel for vehicles, as heating material or as the basis for plastics.

The starting material for petroleum is plankton, which floated in the sea millions of years ago. The remains of these tiny sea creatures sank to the bottom and were buried airtight under other sediment layers, such as sand and clay. The remains decomposed and became putrid mud. Other sediments were deposited on top of it, their weight pressing down on the digested sludge. Under this pressure, the temperature rose and the digested sludge changed chemically into a mixture of gaseous and liquid hydrocarbons: Petroleum. Because it was lighter than water and the surrounding rock, it continued to rise through pores until it encountered an impermeable layer under which the viscous mass collected: a petroleum deposit had been created.

Natural gas was also formed under similar conditions as crude oil. That is why both fuels are often found in one deposit. Natural gas is lighter, which is why it is stored above crude oil. Because both substances are fossil remains of marine organisms, they are called “fossil” fuels.

Coal is also one of the fossil fuels. It owes its origin to the remains of dead marsh plants. These formed increasingly thick layers of peat over which sediments accumulated. Under their weight, water, oxygen and other gases were pressed out of the peat layer, and the proportion of carbon increased. Over thousands of years, the peat thus turned into lignite. If the sediment cover and the pressure continued to grow, lignite became fat coal or hard coal. In order to be able to use their stored energy, the coal deposits – also called coal seams – are extracted in mines.

The outermost shell of the earth

Like an egg from an eggshell, the Earth is also surrounded by a hard shell. This outermost layer surrounds the Earth’s mantle and is called the Earth’s crust. If you compare the earth to a peach, the earth’s crust is – relatively speaking – as thick as its skin. Under continents, it reaches an average depth of 40 kilometres, under the oceans even only about seven kilometres.

Below this lies the outer part of the Earth’s mantle, which reaches down to a depth of about 100 kilometres. It is also solid, but consists of heavier rock. The earth’s crust and this outermost part of the mantle together are also called the “lithosphere”. This solid layer of rock is broken into plates of different sizes that drift very slowly on the hot, viscous mantle.

Where the molten rock from the hot mantle penetrates upwards, the earth’s crust can break open. Lava then flows out and becomes new crust. This mainly happens where the plates of the lithosphere adjoin each other, such as at the mid-ocean ridges.

In Iceland, for example, these plate boundaries are clearly visible: Cracks and furrows run through the earth’s crust here, where the Eurasian and North American plates drift away from each other. There is also a plate boundary in the Mediterranean region. Because the African plate is pressing against the Eurasian plate here, there are many volcanoes and earthquakes in Italy.

The crust is covered by the soil. The soil of the land masses forms from weathered rock and the remains of animals and plants. The seabed, on the other hand, develops from deposits such as clay and the sunken remains of marine organisms. On the coasts, the seabed also consists of deposited debris that has been eroded from the mainland and washed into the sea.