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Learn about rocks, their formation, mining methods, and the useful substances they yield. Explore minerals, metals, weathering process, and the impact of mining on the environment. Discover how rocks are essential resources in various industries.
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Useful substances from rocks What useful substances do we get from rocks?
crust mantle inner core outer core Where do the rocks come from? We get many useful substances from rocks, such as building materials, metals, pigments and jewels. But where do we get the rocks themselves from? They come from the Earth’s crust. The Earth’s crust is the thin outer layer of the Earth. It is about 30km thick on land and only about 8km thick under the sea.
mineral formula metal extracted from it haematite bauxite galena rutile chalcopyrite Minerals and metals Many of the useful substances we get from the Earth’s crust are minerals, which contain metals. Here are the names and formulae of some of the most common minerals. Fe2O3 iron Al2O3 aluminium PbS lead TiO2 titanium CuFeS2 copper
Digging up rocks We get rocks from the Earth’s crust by digging them up in mines and quarries. Do you have any mines or quarries near where you live? What do you think is the impact of a mine or quarry on the local environment?
Slate mining Slate has been mined since Roman times, for use in roofing, flooring, cladding, and architectural products. Penrhyn Quarry, located in North Wales, is thought to be the world's largest slate quarry. A mixture of modern and traditional methods are used to extract the slate, including opencast mining. What impact do you think building the mine has had on the environment? Do you think the benefits of the mine outweigh the costs?
Rocks and weathering Why are rocks all different shapes and sizes?
What is weathering? Rocks are different shapes and sizes because they are changed by the conditions in their environment. The breakdown of rocks into smaller fragments is called weathering. Eventually the fragments become soil. Can you think of anything that could cause weathering? Rocks can be weathered by temperature change, water, frost and even plants and animals.
Types of weathering There are three types of weathering: • physical weathering • biological weathering • chemical weathering. Which type of weathering is caused by each of these: • temperature change • acid rain • plants and animals?
Physical weathering Physical weathering occurs when rock is broken down into smaller pieces by the effects of temperature and water. • Exfoliationweathering (or ‘onion-skin’ weathering) is caused by very hot weather. • Freeze-thawweatheringis caused by the melting and freezing of water. Exfoliation and freeze-thaw weathering tend to occur in very different types of landscapes. Which type of weathering do you think will primarily occur in the desert, and which will occur in the mountains?
Exfoliation weathering Exfoliation weathering is common in very hot and dry places like Uluru (Ayers Rock) in Australia. In these places the daytime temperature can rise above 40°C. While the inner layers of the rocks stay cool, the outer layers of rocks heat up and expand in the baking heat. At night, when the temperature falls, the outer layers of rocks cool down again and contract. Eventually the repeated expansion and contraction of the rock causes the outer layers to peel like an onion skin.
Freeze-thaw weathering When rain water or melted snow seeps into the cracks in a rock and freezes, it can force the crack to expand. When the ice thaws, the rock contracts and the water moves deeper into the crack. Later when the water re-freezes the crack widens again. Over time the crack widens until the piece of rock breaks apart. This slow cycle is called freeze-thaw weathering.
How can freezing water cause damage? You can see freeze-thaw weathering in action if you leave a bottle full of water in the freezer for too long. The water inside the bottle expands as it freezes. The ice that is formed creates huge forces on the bottle, which then cause it to break! Because water expands as it freezes it can create immense pressure in confined spaces. Does this explain why water pipes often burst in winter?
Weathering by plants and animals What are the causes of biological weathering?
Microorganisms and weathering Lichen are a combination of algae and fungi that live together like a single organism. Each organism provides resources that the other benefits from. For example, while the fungus provides shelter for the alga, the alga uses sunlight to make energy, which it shares with the fungus. Lichen slowly break down rocks at the molecular level, using the minerals released from the stone as nutrients.
Plants and weathering Have you ever seen plants growing in the cracks of a pavement, wall or rock? This happens because plants often use the wind to spread out their seeds. When a seed falls into a crack it quickly germinates because of the moist and sheltered conditions. However, as the seedling and its roots grow they put pressure on the crack, causing it to become deeper and/or wider. Plants like ivy cause similar damage because they cling to buildings by root systems that penetrate cracks between bricks.
Animals and weathering Many types of animals, such as rabbits and moles, dig holes to look for food, or to create burrows for shelter. If an animal digs into a crack in a rock it can cause it to shatter, split and break. The rock is then vulnerable to the freeze-thaw process and weathering by plants. When an animal burrows it can also bring buried material to the surface, exposing it to weathering. Rock can also be weathered by animals scratching it with their hooves or teeth while grazing.
Humans and weathering What are some ways in which humans can cause weathering? • Tourism: For example, archaeologists are concerned that ancient sandstone structures, like those found in the city of Petra, a World Heritage Site in Jordan, are being destroyed by people touching,walking and climbing on them. • Vandalism and graffiti.
What is chemical weathering? Slow chemical weathering • Rainwater is naturally a weak acid because carbon dioxide in the air reacts with rainwater to form carbonic acid. • This weakly acidic rain reacts with minerals in rocks and slowly wears them away. Rapid chemical weathering • The burning of fossil fuels produces oxides of sulphur and nitrogen, which make rainwater more acidic. • Acid rain reacts quickly with minerals, so the rocks get weathered more rapidly.
Examples of chemical weathering How has chemical weathering affected these rocks?
by water by wind by glacier Erosion As a rock is weathered, pieces of it fall off. This is called erosion. They will then be transported away by water, wind or glaciers.
What is deposition? Deposition occurs after erosion and transportation. This is the process that occurs when pieces of weathered rock sink to the bottom of the river bed or sea, forming sediment. Eventually this sediment gets so squashed down that it forms new rock, called sedimentary rock.
Transportation by wind Rock particles being transported by the wind cause erosion. Wind erosion has two major effects: • Small particles picked up by the wind are deposited in new places. For example, this is how sand dunes are formed. • When the particles are suspended in the air they can hit objects and cause them to chip and wear down (think of how sand grains sting when the wind blows them against your skin at the beach.)
Transportation by glacier A glacier is a mass of ice that gradually moves overland. As the glacier moves, the stones and rocks in its path become incorporated into the base. The forward motion of the glacier causes the trapped rocks to rotate, scrape and grind along the ground. This friction weathers the landscape and causes valleys and fjords to form. Over time the smaller pieces of rock are carried into the melt water streams that surround the glacier, where they are redeposited on the ground.
