S1 Earth Our Home Chapter 9 PDF

# Chapter 9: Rocks ## Rocky Matter Before advanced technology was available, people in the past made use of materials in their surroundings, such as rocks, to make useful tools. This Hoko knife (a modern model of the original knife) consists of a very small, sharp stone tied to a wooden handle wit...

# Chapter 9: Rocks ## Rocky Matter Before advanced technology was available, people in the past made use of materials in their surroundings, such as rocks, to make useful tools. This Hoko knife (a modern model of the original knife) consists of a very small, sharp stone tied to a wooden handle with a spruce root. The original knife was found near the Hoko River in western Washington. Archaeologists (people who study objects used by people of the past) think that it was used by people who were living there about 2 700 years ago for cutting fish. ## You Will LEARN - about the origins and characteristics of the main rock types - to describe the distribution of the main rock types in Singapore using a map ## Many useful tools of the past were made from rocks. Why do you think rocks were used? ## Look around you. Are there any objects that are made from rocks in your surroundings? Can you describe the appearance of those rocks? ## Of the Earth ### What Are Rocks? Landforms, such as mountains and volcanoes, are made up entirely of rocks. Without rocks, there would be no landforms on Earth. Let us now learn about rocks, what they are made of and how they are formed. Rocks are solid materials of the Earth's crust. They are made up of substances known as minerals, such as quartz and sand. Rocks are formed in various ways, such as when lava cools and hardens on the Earth's surface. Geologists (people who study rocks) have classified rocks into three main types, according to how they are formed. The three types are igneous, sedimentary and metamorphic rocks. **Igneous Rocks** 1. Basalt - Uses: Floor tiles, basalt fibres and textiles 2. Granite - Uses: Buildings, monuments **Sedimentary Rocks** 3. Limestone - Uses: Cement, blackboard chalk 4. Shale - Uses: Raw material for making pottery and tiles 5. Sandstone - Uses: Construction, raw material for making pottery **Metamorphic Rocks** 6. Marble - Uses: Architecture, ornaments 7. Slate - Uses: Roofing sheets, table tops ## Igneous Rocks The word 'igneous' comes from the Latin word ignis, which means 'fire'. Does this give you a clue as to where igneous rocks come from? Remember that magma, a very hot molten material, makes up the Earth's interior. Geologists describe igneous rocks as magma that has cooled and hardened, either beneath or above the Earth's surface. **Coarse-grained Igneous Rocks:** are formed when magma cools and hardens inside the Earth. **Fine-grained Igneous Rocks:** are formed when lava cools and hardens on the Earth's surface. ### Coarse-grained igneous rocks The appearance of igneous rocks is affected by how fast magma cools. When magma cools and hardens slowly in the Earth's interior, coarse-grained igneous rocks are formed. This means that we can see individual grains on the rocks with the naked eye. An example of a coarse-grained igneous rock is granite. Granite can be used to make many things, such as pavements and stone walls. ### Fine-grained igneous rocks When lava cools and hardens quickly on the Earth's surface, fine-grained igneous rocks are formed. The individual grains are very small and a microscope is needed to see them in detail. An example of a fine-grained igneous rock is basalt. Basalt is very hard and resistant to weathering. It can be used as a material for floor tiles and basalt fibres. Basalt fibres are used in the construction industry to make concrete stronger. ## Sedimentary Rocks Weathering and erosion cause rocks to break down into smaller pieces. Tiny pieces of broken rocks, together with grains of sand, clay and silt, are known as sediments. Being small and light, sediments are easily carried away by wind and water. Eventually, some of the sediments are deposited into rivers and oceans. As the sediments pile up in layers, the weight of the layers on top presses down on the layers below. Eventually, the sediments cement together and harden. These solid, hardened layers of sediments are called sedimentary rocks. The appearance of sedimentary rocks depends on the type and size of the sediments. When the sediments are very small, fine-grained sedimentary rocks are formed. An example of a fine-grained sedimentary rock is shale, which is often used to make bricks. With larger sand-sized particles, coarse-grained sedimentary rocks are formed. An example of a coarse-grained sedimentary rock is sandstone. Another example is conglomerate, which is a mixture of pebbles and sand grains cemented together. Not all sedimentary rocks, however, are formed from sediments. Some are formed from the hardened remains of animals and plants. An example of such a sedimentary rock is limestone. Some types of limestone are made up of the remains of coral, shell and even bone. Limestone may also contain fossils, which are the preserved parts of marine animals and plants that lived long ago. ## Metamorphic Rocks Sedimentary and igneous rocks sometimes become completely transformed or changed under intense heat and pressure. This could occur due to crustal movements or when the rock comes into contact with molten magma. When that happens, metamorphic rocks are formed. The word metamorphosis is the Greek word for 'transformation'. For example, when an igneous rock like granite is subjected to extreme high temperatures and intense pressure, it transforms into a metamorphic rock called gneiss. Under similar conditions, sedimentary rocks like shale changes into slate, whereas limestone changes into marble. ### Metamorphic Rocks Heat and pressure sometimes cause metamorphic rocks to have a foliated appearance, that is, to have bands. Slate is an example of a metamorphic rock with a foliated texture. This means that the different minerals are aligned in parallel layers. It is formed from shale, a sedimentary rock. Metamorphic rocks can be used as materials for buildings and decorations. For example, marble is commonly used as a building material in homes, and as a sculpting material by artists. Slate is often used as a construction material for fireplaces and flooring. ## The Rock Cycle The three main types of rocks are interrelated in the ways they are formed. Over time, one type of rock can change into another. Rocks of any type that are broken into pieces may form sedimentary rocks. Igneous and sedimentary rocks may change into metamorphic rocks. Metamorphic rocks sometimes get buried deep in the Earth where there is intense heat and pressure. They melt and become magma, which then cools and hardens to form igneous rocks. Hence, rocks constantly undergo a cycle of change. This continual process of change in rocks is known as the rock cycle. ## Main Rock Types in Singapore We have learnt that rocks are classified into igneous, sedimentary and metamorphic. All the three types of rocks are present in Singapore. Igneous rocks make up the central part of Singapore, while sedimentary rocks occupy the eastern and western parts of the island. A small area of metamorphic rocks is located in Pulau Tekong. ### Igneous Rocks in Singapore The type of rock most commonly seen in Singapore is granite. It is located largely in the central part of Singapore, in the area known as the Bukit Timah Granite Formation. This large area of granite measures some 8 kilometres from north to south and 7 kilometres from east to west. ## Sedimentary Rocks in Singapore We can find different types of sedimentary rocks in the southern, eastern and western parts of Singapore. Rocks in these parts are layered, consisting of mainly sandstone and conglomerate. ## Metamorphic Rocks in Singapore We can find a small area of metamorphic rocks called the Sajahat Formation on Pulau Tekong. The rocks here are formed under intense heat and pressure, and are very hard. ## Rocks in Our Environment Rocks are present everywhere in our physical environment. Besides being the building blocks of landforms like mountains and volcanoes, rocks are used by people to build structures like buildings and roads. ## What It Means - An **igneous rock** is a rock formed from magma that has cooled and hardened beneath or above the Earth's surface. - A **metamorphic rock** is a rock that is completely transformed or changed from an igneous or sedimentary rock under intense heat and pressure. - A **rock** is a solid material of the Earth's crust, and is made up of substances known as minerals. - The **rock cycle** is the continual process by which rocks change from one type to another. - A **sedimentary rock** is a rock formed by the cementing and hardening of layers of sediments under pressure from the overlying layers. ## Got It Covered This diagram illustrates the processes that result in the formation of igneous, sedimentary and metamorphic rocks. ### Formation of Sedimentary Rocks - Weathering and erosion break down rocks to produce sediments. - Layers of sediments are pressed and cemented together, and hardened to form sedimentary rocks. ### Formation of Igneous Rocks - Lava cools and hardens quickly on the Earth's surface to form fine-grained igneous rocks. - Magma cools and hardens slowly inside the Earth to form coarse-grained igneous rocks. ### Formation of Metamorphic Rocks - Intense heat and pressure cause igneous and sedimentary rocks to change into metamorphic rocks.