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Different types of rock There are many different types of rocks in the world. 3 of 47 © Boardworks Ltd 2008

Identifying rocks 4 of 47 © Boardworks Ltd 2008

Identifying rocks: summary type examples sedimentary sandstone and limestone metamorphic igneous 5 of 47 marble and slate basalt and granite description the softest rock type, containing layers and sometimes fossils usually harder than sedimentary rocks, containing thin layers and twisted fossils usually the hardest rock type, containing shiny crystals © Boardworks Ltd 2008

Different rocks = different uses 6 of 47 © Boardworks Ltd 2008

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Pancake rocks in New Zealand These limestone rocks at Punakaiki in New Zealand are known as the Pancake Rocks. How do you think they were formed? 8 of 47 © Boardworks Ltd 2008

What are sedimentary rocks? chalk limestone sandstone 9 of 47 © Boardworks Ltd 2008

Properties of sedimentary rocks What are the properties of sedimentary rocks? l Sedimentary rocks often have layers showing the deposition of sediment at different time periods. l Sedimentary rocks are made of lots of small grains. These grains are weakly held together so the rocks are often porous and may be soft and crumbly. l Sedimentary rocks often have fossils trapped within them. 10 of 47 © Boardworks Ltd 2008

Comparing ages of sedimentary rocks Why are sedimentary rocks near the surface younger than sedimentary rocks deeper down? 11 of 47 © Boardworks Ltd 2008

Forming sedimentary rocks 12 of 47 © Boardworks Ltd 2008

How are fossils formed? When small rock fragments are transported to the sea, they are deposited (sink) and form a sediment. Dead creatures may become trapped within the sediment. Over millions of years, the pressure of layers above cements the sediment together. This is how sedimentary rocks like sandstone, mudstone and limestone are formed. As the body of the creature decays away, its shape is left imprinted in the rock, forming a fossil. 13 of 47 © Boardworks Ltd 2008

Formation by evaporation of water Sedimentary rocks can also be formed from minerals that are left behind when water evaporates. l Some minerals are dissolved in seas and lakes. l Over millions of years these seas or lakes dry up. l As the water disappears, the dissolved minerals are left behind. l Chalk and limestone, common in the UK, can be formed in this way. 14 of 47 © Boardworks Ltd 2008

Which type of sedimentary rock? 15 of 47 © Boardworks Ltd 2008

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What are metamorphic rocks? What has happened to the fossils and layers of particles in these rocks? The layers and fossils in these rocks have become squashed and twisted. What caused this? 17 of 47 © Boardworks Ltd 2008

Formation of metamorphic rocks Sedimentary rocks are turned into metamorphic rocks by the extreme pressures and temperatures deep within the Earth. These conditions change the structure of the rocks so that new layers are formed. heat more heat pressure more pressure Mixture of grains in structure 18 of 47 Heat and pressure compress grains Grains form orderly layers © Boardworks Ltd 2008

Properties of metamorphic rocks How are the properties of metamorphic rocks different from sedimentary rocks? l Metamorphic rocks often contain layers of crystals, caused by the effect of heat and pressure. l Metamorphic rocks are usually denser and harder than sedimentary rocks. l Metamorphic rocks sometimes show wavy or zig-zag patterns within the rock, caused by the movements that led to their formation. 19 of 47 © Boardworks Ltd 2008

Examples of metamorphic rock marble soap stone slate 20 of 47 © Boardworks Ltd 2008

What is marble? Marble is a hard smooth rock made from sedimentary limestone or chalk. Because marble is extremely hard it is an excellent building material, and is also often used for sculpture. The different colours in marble are caused by the different combinations of minerals in the limestone from which it was formed. 21 of 47 © Boardworks Ltd 2008

What is slate? Slate is a grey rock with fine grains made from sedimentary volcanic ash or clay. Because it is composed of many distinct layers, slate can be split into thin sheets. During the 18 th and 19 th centuries, thin sheet of slate were used as a writing surface. Slate sheets have also traditionally been used as a roofing material. 22 of 47 © Boardworks Ltd 2008

What is mica? Mica is a mineral that forms sheets that split smoothly, creating almost perfect edges. This is because its atoms are arranged in hexagonal sheets. Mica usually appears very shiny. Because of its stable atom arrangement mica is very heat resistant. For this reason it is often used in electrical components such as capacitors, and as an insulator in high voltage equipment. Because mica can be split into flat sheets it is also often used an alternative to glass window panes in greenhouses etc. 23 of 47 © Boardworks Ltd 2008

Which type of metamorphic rock? 24 of 47 © Boardworks Ltd 2008

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What are igneous rocks? The name “igneous” comes from the Latin word for fire. Where do you think this suggests that igneous rocks are formed? Igneous rocks are formed in, and around, volcanoes. What are some examples of igneous rocks? basalt 26 of 47 pumice © Boardworks Ltd 2008

How are igneous rocks formed? Magma is a type of molten rock found deep underground. Occasionally magma rises up through the Earth’s surface, causing volcanic eruptions. Igneous rocks are formed when the magma cools and solidifies. l When magma cools above the surface, extrusive igneous rocks are formed. l When magma cools below the surface, intrusive igneous rocks are formed. 27 of 47 extrusive igneous rock intrusive igneous rock magma © Boardworks Ltd 2008

Properties of igneous rocks How are the properties of igneous rocks different from metamorphic and sedimentary rocks? l Igneous rocks contain interlocking crystals that are held together very strongly and make the rock hard. l The crystals in igneous rocks have a disorderly arrangement. l The size of the crystals depends on how quickly the igneous rock solidifies. l Igneous rocks never contain fossils. 28 of 47 © Boardworks Ltd 2008

Crystal size in igneous rocks 29 of 47 © Boardworks Ltd 2008

Crystal size in igneous rocks Magma is full of minerals that turn into crystals under the right conditions. Magma above the Earth’s surface cools quickly, causing only small crystals to form. This is how extrusive igneous rocks like pumice and basalt are made. Magma below the Earth’s surface cools more slowly. There is time for large crystals to grow as the magma solidifies. This is how intrusive igneous rocks like granite are formed. 30 of 47 © Boardworks Ltd 2008

What is granite? Granite is an intrusive igneous rock. It is an extremely hard rock, and contains many large crystals. Granite is found all over the world, but is commercially quarried in India, Brazil, South Africa and Scandinavia. Because it is so hard granite is often used as a flooring and exterior cladding material, as well as decorative material in worktops in kitchens and bathrooms. 31 of 47 © Boardworks Ltd 2008

What is pumice? Pumice is a pale grey extrusive igneous rock, made up of very small crystals. It is formed when bubbles of volcanic gas pass through magma as it solidifies. Because of this, pumice contains many air pockets, making it extremely light and porous. These lightweight properties mean that pumice is often used as a component in breeze-block bricks. Its rough surface also means that it is useful as an exfoliating (scrubbing) tool. 32 of 47 © Boardworks Ltd 2008

What is basalt? Basalt is a dark glassy extrusive igneous rock. Basalt contains very small crystals, and is often found in nature as huge columns of rock. Traditionally basalt has been used to make weapons, tools, jewellery and carved sculptures. Today basalt is also used in the production of cement and road surfaces. 33 of 47 © Boardworks Ltd 2008

Working with rocks Geologists are scientists who study rocks. They look at rocks and use their observations to draw conclusions about the Earth. l Some geologists study rocks to learn about the history of the Earth and how it was formed. l Some use their work to try to find deposits of valuable minerals and fossil fuels. l Others try to predict earthquakes, tsunamis and volcano eruptions. 34 of 47 © Boardworks Ltd 2008

Working with volcanoes Scientists who study volcanoes are called volcanologists. They are skilled at monitoring the changes in active volcanoes that can indicate when an eruption might occur. Monitoring equipment is very expensive and there are not enough resources to keep check on every active site in the world. This can make studying volcanic activity quite a challenge. 35 of 47 © Boardworks Ltd 2008