Grouping rocks. Look at all the different forms of rocks in these photographs. See the variation in shape and colour.

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1 Grouping rocks Rock is made of grains that fit together. Each grain in the rock is made from a mineral, which is a chemical compound. The grains in a rock can be different sizes, colours and shapes. Some types of rock have interlocking grains that fit tightly together, for example granite. Rocks such as marble and slate do not let water soak through them. They are called impermeable rocks. Other types of rock have rounded grains, for example sandstone. These are usually softer and more crumbly than rocks with interlocking grains. Rocks with rounded grains are more likely to absorb water than rocks with interlocking grains. This is because the water can get into the gaps between the grains. Rocks that absorb water are called porous. Some rocks, such as sandstone or chalk, let water soak through them. They are called permeable rocks. Wherever you are standing, there are rocks underneath you. If you are standing in your garden, walking in the park, building a sandcastle on the beach, swimming in the sea or crossing a river, there are rocks somewhere beneath your feet. Rocks come in many different forms, from soft mudstone and crumbly sandstone to hard granite. Some rocks split across in sheets - like slate. Other rocks are rare and valuable - like gold and diamonds. Look at all the different forms of rocks in these photographs. See the variation in shape and colour. Parents in Touch Page 1 of 5

2 So why do we see earth and stones? Rocks break down - ice cracks them; water erodes them. They are rubbed together and break into smaller and smaller pieces. These small bits are mixed with the remnants of plants and animals and make earth or soil. Rocks can be divided into three types: 1. Igneous rocks are formed from molten material called magma that comes from deep inside the Earth. Sometimes this material cools slowly under the surface, but sometimes it explodes out from a volcano as liquid lava. Igneous rocks are also called volcanic rocks. At one time the whole of the Earth s crust was formed from igneous rocks. It has taken millions of years for the other types to be formed. The changing of rocks from one form into another is called the rock cycle. Igneous rocks include: Basalt Dolerite Granite Obsidian Pumice Rhyolite Basalt 2. Metamorphic rocks are formed from igneous and sedimentary rocks that have been changed in some way by heat or pressure inside the Earth. The elements that make up the rocks may be remixed, but no new ones are added or old ones taken away., for example, is a changed form of limestone. Metamorphic rocks include: Gneiss Mylonite Schist Slate 3. Sedimentary rocks are formed from the remains of older rocks that have been worn away. Layer upon layer of rock pieces may be gathered together in one place by water, wind or ice. Many were originally part of the sea bed and also contain fossils of shells and tiny sea creatures. Over thousands of years, the weight of the layers above presses the bottom layers together so hard that they join together into solid rock again. Sedimentary rocks include: Conglomerate Limestone Sandstone Parents in Touch Page 2 of 5

3 Use the websites listed below to help you complete this table. Name of rock Granite Description (use the Word Bank to help you) Where did you see it? What is it used for? Why is it used for this? Pumice Slate Limestone Word Bank smooth rough hard soft dull shiny light heavy porous grainy strong brittle sharp crystalline black white grey brown red yellow orange crumbly Further information and research This is a useful website that shows pictures of various rocks, divided into igneous, sedimentary, metamorphic and minerals. Parents in Touch Page 3 of 5

4 Learn about the rock cycle here This site is full of information about rocks. Minerals Minerals are the ingredients that make up rocks. They may be composed of a single element, such as gold or copper. These are called native elements. Other minerals are made of compounds of elements. Parents in Touch Page 4 of 5

5 Properties of minerals Each type of mineral has its own combination of properties that identify it. Some of the properties are: Colour Many minerals come in a wide variety of colours. Different minerals can be the same colour. Crystal form describes the geometric shape of a crystal. Hardness is the resistance of a mineral to scratching. Lustre is how a mineral reflects light or how it shines. Some ways to describe lustre include glassy or vitreous, metallic, dull, and pearly. Magnetism is a special property of some minerals, especially magnetite. Samples are attracted by a magnet. Lodestone, a special form of magnetite, is a magnet itself. Streak is the colour of a mineral in powdered form. Transparency describes how a mineral transmits light. Some minerals are transparent (you can see through them); others are translucent (some light passes through a sample) or opaque (no light passes through a sample). Parents in Touch Page 5 of 5