Are igneous stones expensive


It crumbles, splinters and weathered: the ravages of time are gnawing at Cologne Cathedral. Acid rain has already eroded the famous building. Air pollution laws have been reducing pollution for a number of years. But pigeon droppings, exhaust fumes and the weather continue to affect the old walls and never let the craftsmen of the cathedral builder become unemployed.

The foundation stone of Cologne Cathedral was laid on August 15, 1248. Since then, around fifty different rocks have been set into the Rhenish sand here. The builders only built many of them on a trial basis; not every stone could withstand the weather. In addition, the rock had to come from close by, as transport was incredibly expensive in the Middle Ages. As a result, the cathedral consists mainly of trachyte, shell limestone, sandstone and basalt. The calcareous sandstones and shell limestone are particularly susceptible to weathering and environmental influences. These are already badly pitted. In order to save the sensitive shell limestone from weathering, various protective coatings were tried out. That should at least slow down the crumbling. In contrast, the trachyte from the Drachenfels has held up well. The basalt rocks are also weatherproof and in good condition to this day.

Despite all efforts, components have to be replaced again and again. Every year 15 to 20 cubic meters of natural stone are used to preserve the famous church building. Even if the Cologne Cathedral was already built in 1880: The stonemasons of the cathedral building have their hands full to this day!

Stone intolerance

The Cologne Cathedral evidently weathers more than other comparable buildings. Conservationists now have a guess as to why that is so: The cathedral is built from many different types of stone. And not all rocks get along with each other. For example, the damage is particularly severe where trachyte from Drachenfels meets sandstone from Obernkirchen. A research group is now to find out whether and why some rocks actually damage each other and which of them can get along well with each other.

constant dripping wears away the stone

Deep gorges in the mountains, wide sandy beaches by the sea and wide rivers that meander through meadows and fields - all of these are landscapes that we know well. Because they are so varied, we find them impressive and beautiful.

The sculptor of all these landscapes is the water cycle. Sooner or later, water forms the surface of the earth more strongly than any other force. It washes away soil after a downpour. It digs into the ground and loosens parts of the rock. It carries earth and weathered rock debris with it down into the valley. Where the water drains off more slowly, it lets go of its burden of silt, sand and rubble. When there is high water, it floods the flat areas of a valley, the river meadows. Here, too, it deposits fine mud. When the water finally flows into the sea, it works the coasts and forms very different landscapes, for example cliffs or long sandy beaches.

Water also shapes the landscape in the form of ice. If water freezes in cracks in the stone, it bursts the stone. As a glacier, it planes out notch-shaped river valleys to form round trough valleys. And the moraine landscape in the foothills of the Alps with its boulders and boulders is the result of glaciers that formed the subsoil a long time ago.

Wind erosion - From shifting dunes and mushroom rocks

Wherever wind sweeps over sandy, dry ground, it drags fine grains with it and later drops them again. In this way, sand hills pile up - the dunes. Such sand dunes are mainly found in arid deserts such as the Sahara, the Gobi or the Namib Desert. Their dunes can be over 200 meters high and many kilometers long.

To see a dune, you don't have to go into the desert at all: there are also dunes on the coasts, in Germany for example on the North or Baltic Sea coast. The sand that is blown away from the beach by the wind piles up inland to form dunes. If you want to go to the beach, you often have to find a way through or over the dunes.

Some dunes hardly move from the spot, for example when they are overgrown with beach grass. Others, on the other hand, roll forward in the direction of the wind, like the waves of the sea, the shifting dunes. The Rubjerg Knude on the coast of Denmark is a particularly fun dune. This almost 100 meter high dune is moving towards the northeast and has even rolled over a lighthouse on its journey.

Dunes have different shapes. Some are curved like crescents or sickles - the sickle dunes. Others form a wall across the direction of the wind, the transverse dunes. Both rise slightly on the windward side. On the side facing away from the wind, they fall steeply down. And some dunes even start their own song: When sand avalanches break out of the dune and the grains of sand collide, they make humming or humming noises: The dune is "singing"!

But wind and sand don't just form dunes. Flying grains of sand can grind rocks in the landscape like sandpaper. Even hard rock can get a new shape through this wind grinding: Towering rocks are scraped off and hollowed out at their feet over time. Finally they tower up like mushrooms - a mushroom rock has emerged.

From rock to grain of sand - weathering

Today the north of Canada is a gently undulating landscape. However, many millions of years ago there was a mountain range here. In fact, even high mountains can turn into small hills over a very long time.

The reason for this transformation: The rock on the earth's surface is constantly exposed to wind and weather. For example, if water penetrates into cracks in the stone and freezes, it splits the stone apart. This process is called frost blasting. The rock also becomes brittle through temperature changes between day and night and through the force of water and wind. In other words: it weathers. This process can also be observed on buildings or on stone figures. During the weathering, the rock breaks down into smaller and smaller components up to fine grains of sand and dust. Different rocks weather at different rates: Granite, for example, is much more resistant than the comparatively loose sandstone.

Some types of rock even completely dissolve when they come into contact with water, for example rock salt and lime. Rock salt is chemically the same as table salt - and that already dissolves in ordinary water. Lime is somewhat more stable, but limestone also dissolves in acidic water. Acid is formed, for example, when rainwater in the air reacts with the gas carbon dioxide. This “acid rain” attacks the limestone and dissolves it over time. The weathering leaves rugged limestone landscapes on the surface of the earth, and caves are formed below the surface.

But not only solution weathering, heat and pressure also wear down and crumble rock under the earth's surface. Wherever plants grow, roots dig in, break up the rock piece by piece and also ensure that it is removed millimeter by millimeter.

In this way, weathering not only works on individual rocks, it gnaws at entire mountain ranges. It will take a few million years for the Black Forest to be as flat as northern Canada.

What causes erosion?

When rock weathers, it seldom remains in its original location. Rock debris often rolls down the slope, is washed away by the water or pushed away by masses of ice. The wind can also carry fine rock dust or sand with it. Regardless of whether the rock is removed by water, ice, wind or gravity, all of these processes are called "erosion".

The erosion by running waters is particularly drastic. Streams and rivers dig a bed in the ground, rock slides down, a valley forms. If a glacier rolls down the valley, it planes this valley wider through the scree it has carried along with it. Long after the ice has melted, you can tell from such trough valleys that there was a glacier here. The surf of the sea, however, attacks the coast. Steep cliffs are hollowed out and collapse, sandy beaches are washed away by the waves. In deserts, the wind sweeps away large areas of sand. The harder it blows, the more sand it can take with it. A sandstorm gradually removes obstacles made of solid rock like a sandblasting fan.

When rain and wind wash or blow away the soil cover over large areas, we speak of soil erosion. Soil erosion is also used in the case of landslides on slopes. The problem: The fertile upper layer of the soil disappears. In the worst case, it can no longer be used for agriculture.

If the soil is overgrown with plants, this slows down erosion. The roots of the plants hold the soil in place and prevent the wind and water from carrying it away. If the plant cover is destroyed, for example by deforestation, the soil lacks this support and it is eroded.

Sedimentary rocks

Some rocks look like they're striped. In the Dolomites, for example, such transverse bands can often be clearly seen. Sandstone or limestone quarries sometimes have similarly pretty patterns.

The "stripe design" is created when the rock is formed. The starting material is weathered debris that is carried away by water or the wind. Rivers, glaciers and dust storms lose their strength at some point: the courses of rivers become slower and slower towards the mouth and finally flow into the sea or a lake. Glaciers are advancing into warmer regions and melting. Dust storms also subside at some point. Then they can no longer move dust, sand and rubble. The crushed rock that is dragged along settles out. Over time, the deposited material forms an ever higher layer - the sediment. Such sediments, including the remains of dead animals or limestone shells, collect particularly on the seabed and on the bottom of lakes, where rivers wash up a lot of material.

Gradually, different sediments are layered on top of each other. A layer can, for example, consist of sandstone: During the dry season, the wind blew desert sand here. If the sea level rises again, this layer is covered by water: the limestone shells of marine animals sink to the sea floor and deposit another layer over the sand. Over millions of years the climate changed again and again and caused the sea level to fluctuate. This allowed different layers to deposit.

Over time, the sediment cover becomes thicker and thicker. Under the weight of one's own weight, the initially loose sediments are compressed more and more, small cavities disappear, the mass condenses. Further layers are deposited over it, the sediment becomes more and more solid and finally becomes sedimentary rock under pressure. This process is also called diagenesis in geology. For example, if the shells of tiny marine animals are pressed into stone, limestone is created. Fine grains of sand made of quartz cement together under the high pressure to form sandstone.

In addition to rubble, dead animals also settled, for example fish on the sea floor. Their bones and scales remained hermetically sealed and petrified. Such fossils are immortalized in the stone. Even after millions of years, they reveal a lot about the time in which the sediment was formed. Therefore, geologists can read in the rock layers like a history book.

Usually only the top layer is visible to us. However, when a river digs its way through the sedimentary rock, lifts it up during mountain formation, or blasts it free in a quarry, we get a glimpse of the cross-section. The individual layers of sediment can then be easily recognized as "stripes" or bands in the rock.

Igneous rocks

Biting granite means that something is hopeless. Because of its great hardness, granite can not only be used as a phrase, but also as a paving stone or for building walls. Granite is a rock that lies over two kilometers below the earth's surface and is common in the earth's crust.

Granite is formed when glowing magma solidifies when it cools. The dark spotted gabbro or monzonite are also formed from slowly cooling magma. If this process takes place deep inside the earth, geologists speak of Deep rock, also Plutonite called.

If, on the other hand, the hot rock slurry penetrates outwards during a volcanic eruption and pours over the surface of the earth, it is from Effluent rock or Volcanite the speech. The volcanites include the light pumice stone, the porous tuff or the rhyolite, which was formed from the same material as granite, but has a different structure and is less hard because it cools faster on the surface of the earth than the granite in the depths. Basalt is also a volcanite. Sometimes it freezes into hexagonal, closely spaced columns that look as if they have been cast into shape. Basalt forms on the surface of the earth from the same mass as the gabbro in the depths.

Vulcanites weather immediately after their formation, plutonites only when the overlying rock layers have been eroded. Because both volcanites and plutonites became rock from cooled magma, both are classified as igneous rocks.

Metamorphic rocks

It happens inside the earth: Strong pressure and high temperatures ensure that the constituents of the rock, the minerals, react with one another and transform. In this way new rock is formed. Because the Greek word for metamorphosis is “metamorphosis”, geologists also speak of metamorphic rocks.

A correspondingly high pressure is created when two earth plates collide and one plate dips under the other. The rock is then squeezed together like in a huge press. A frequent result of such a rock metamorphosis is the blue schist. Its parent rock is basalt or a rock with a similar composition to basalt.

Extreme heat also causes rocks to transform. For example, it is baked near a magma stove like in an oven. Marble, for example, is nothing more than limestone that has been heated very strongly in the interior of the earth; During this process, new minerals are formed and the rock becomes harder. Sandstone also changes at high temperatures, because its quartz grains then stick together: the harder quartzite is made from the original sedimentary rock.

In contrast to the complete melting through volcanism, the rock remains solid during the metamorphosis. However, if the temperature continues to rise, the rock will eventually turn into liquid magma. If this mass cools down, it turns into igneous rock. The rock cycle is in full swing.

Cycle of rocks

No rock on earth is made to last. It weathers on the surface, is removed and redeposited. When two plates collide, layers of sediment are compressed and unfolded to form high mountains. The rock of submerged plates melts in the earth's interior and forms the source of volcanoes. Lava that spits out from a volcanic crater cools down and solidifies again into rock.

It is an eternal cycle that ensures that even the hardest rock is constantly changing and new things are created from it. The transformation does not happen overnight, of course, but over millions of years. "Players" in this cycle are three groups of rocks, each of which is formed under different conditions:

When magma cools, the hot mass solidifies igneous rock. This can happen both on the surface of the earth and inside the earth. On the other hand, where layers of excavated rock pile up, the sediments are compressed under the weight of their own weight. This pressure causes them to solidify Sedimentary rock. In turn, high pressure and great heat in the earth's interior ensure that rock is transformed and another is created. Then geologists speak of transformation or of metamorphic rock.

These three types of rock are closely related: each type can transform into any other. This rock cycle will continue as long as the earth exists.


For hours yesterday, two tourists were trapped on a rock in the raging sea. One of the two arches of the rock sculpture “London Bridge” on Australia's famous “Great Ocean Road” suddenly collapsed. As a result, the way back was cut off for the visitors. They had to be rescued by a helicopter.

The young couple had walked to the end of the second arch to enjoy the fantastic view of the sea and coast. Once there, they heard an ominous crunch. When they looked around, the arch had already collapsed, cutting off the connection to the bank. Fortunately, no one was on the first arch, and there were no other victims. After five hours of waiting, the couple were happily brought back ashore by helicopter.

The double arch of "London Bridge" was one of the most famous rock formations on Australia's south coast. Wind and waves carry away this coast more and more and made sure that part of the tourist attraction collapsed. After the collapse, the "London Bridge" was renamed without further ado: It is now called "London Arch".

On the "Great Ocean Road"

The surf on Australia's south coast, along which the famous Great Ocean Road runs, is wild. The stormy seas have already claimed many victims here: Over a hundred ships have already crashed into the rocky coast. Wind and waves grind everything that gets in their way. And that is above all the relatively soft limestone with its bizarre rock colossi: London Bridge was just one of them, the "Twelve Apostles" or the "Island Archway" are also world-famous. The collapse of “London Bridge” shows how fragile the coast is: The rock crumbles in the raging sea, almost like sugar in hot tea. Without a break, the forces of nature gnaw at the coast and redesign it. So if you want to see the twelve apostles in full splendor, you should hurry.