KS3 Chemistry Rocks

Can you remember? What the three naturally forming types of rocks are Why the water turns things to stone? What happened when the viaduct collapsed in 1848? How the cave was formed? What the name for people who study how rocks form is?

Granite has interlocking grains Sandstone has rounded grains Let’s rock it! Rocks are 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 colours, shapes and sizes. Granite has interlocking grains Sandstone has rounded grains

Can you guess which is which? Porous rocks... 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. Rocks with rounded grains are usually softer and more crumbly than rocks with interlocking grains. So porous rocks tend to be softer than non-porous rocks. Can you guess which is which?

We are going to test two different rocks to see whether or not they are porous and therefore have interlocking or rounded grains... 1. Put each rock in a measuring jug and add water to 300ml. 2. Leave them for 45 minutes and then see if the water has gone down. How much has the water gone down in ml? What does this mean?

Can you remember? How is sedimentary rock formed? Sedimentary rocks are formed over millions of years when sediments (tiny pieces of rocks and animal skeletons) are pressed together at the bottom of seas and rivers. Examples include sandstone, coal and chalk. They are porous. How is igneous rock formed? Igneous rock is formed when magma or lava from volcanoes cools and from this they contain crystals. Examples include basalt and granite. Most igneous rocks are very hard. How is metamorphic rock formed? Metamorphic rocks are formed when other rocks are changed due to immense heat or pressure. Examples include slate and marble.

Describe the rock cycle to your partner

If I were… a sedimentary rock Describe the properties and examples.

If I were… a sedimentary rock I would have been laid in layers at the bottom of a lake or the sea. I am usually light in colour. I would be formed from layers of sediment. I could be sandstone. I could contain fossils of dead plants or animals. If I were… a sedimentary rock I would have been squashed and compacted over many years. I could be limestone. My layers would have been cemented together by other minerals. I could be chalk. I am often grainy and crumbly in texture.

If I were… a metamorphic rock Describe the properties and examples.

If I were… a metamorphic rock I would have been under a lot of pressure and heat for a long time. I could contain small crystals. I am probably very hard. If I were… a metamorphic rock I would have changed from a sedimentary rock. I could be marble. I could be slate. I could have wavy and twisted layers.

If I were… an igneous rock Describe the properties and examples.

If I were… an igneous rock If I cool slowly underground I would be an intrusive rock. If I cool quickly, the crystals will still only be small. The magma would likely have cooled after being pushed onto the crust through volcanoes. Lava is molten rock above ground. I would be formed from molten rock (magma) that is cooled down. If I were… an igneous rock If I cool quickly above ground I would be an extrusive rock. If I cool slowly, the crystals have time to grow bigger. I would contain lots of different minerals and crystals of different sizes. I could be granite (intrusive). I could be basalt (extrusive). Magma is molten rock underground.

Test yourself! https://www.bbc.co.uk/bitesize/guides/zgb9kqt/test

Further ideas for sedimentary, igneous & metamorphic rocks... Gather a range of rocks and the students sort them into the three categories according to their properties. Bake the different rocks! Create the formation of the different rocks using chocolate chips, marshmallows, coconut flakes etc. Can also use crayons and heat to similarly illustrate the layers and grains. Students investigate what rocks are formed in different places across the world.