Igneous rock Tuesday, 06 November 2018 Learning objectives: To describe how the crystal size in igneous rocks changes with the time taken for the rocks to cool.

Igneous rock Starter Display two pictures on the board: one of a small uncut diamond and one of a large uncut diamond. Provide two sticky labels: ‘5000 years’ and ’50 000 years’. Ask students which diamond belongs to which label and why.

Igneous rock Activity 1 Small uncut diamond Large uncut diamond

Igneous rock Activity 2 Cooling magma 1 Tell students the granite they have just examined was formed when magma – liquid rock – cooled and solidified. Link this to the wax volcano model demonstration from lesson 8.1a, in which wax cooled and solidified. [Note: in the volcano model, the wax was in contact with water, so it cooled and solidified quickly. This is analogous to the formation of basalt, which forms mainly under the sea. Granite is formed when magma cools slowly underground.]

Igneous rock Tell students they will now study another model that illustrates, in more detail, how granite and some other rocks were formed. Each pair collects two microscope slides, a pipette, a dark piece of card or paper, and 5 g of Salol in a boiling tube partially immersed in a beaker of hot water. Tell them to put one of the slides on their dark paper. They use a teat pipette to put a few drops of liquid Salol on it. Place the other slide on top. Carefully observe what happens, both through the hand lens and with the naked eye.

Igneous rock Activity 3 – Cooling magma

Igneous rocks are formed from magma.

Igneous Rocks Igneous Rocks

Igneous rock Big crystals or small? Magma cools more quickly on the surface to make rocks with smaller crystals. These are extrusive igneous rocks. Magma cools slowly underground to form rocks with big crystals. These are intrusive igneous rocks. Captions: <Magma cools slowly underground to make rocks with big crystals. These are intrusive rocks.> <Magma cools more quickly on the surface to make rocks with smaller crystals. These are extrusive rocks.>

Igneous Rocks Igneous Rocks

Rocks are a mixture of minerals. Igneous rock Rocks are a mixture of minerals. Minerals are elements or compounds that occur naturally in the Earth. They usually have a crystal structure. Rocks are made up of a number of minerals.

Rocks are a mixture of minerals. Igneous rock Rocks are a mixture of minerals. Caption: <This granite is a mixture of 4 minerals: quartz (grey crystals, calcium feldspar (white crystals), biotite (black crystals) and potassium feldspar (pink crystals).>

Most igneous rocks are… …hard and strong

…and non-porous (water doesn’t soak into them) Igneous rock …and non-porous (water doesn’t soak into them)

Granite is hard, strong and non-porous Igneous rock Granite is hard, strong and non-porous That’s why it makes great kerbstones… … and kitchen worktops

Basalt was formed when magma cooled quickly, say under the sea. Igneous rock Basalt was formed when magma cooled quickly, say under the sea. So basalt has small crystals – you need a hand lens to see them.

Igneous rock Activity 4 Identifying igneous rocks Students examine at least 6 rock samples, perhaps arranged as a circus. From them, they use what they have learnt in the PowerPoint to identify the two igneous rocks. Through discussion, check that all students correctly identified the igneous rocks, and ask a few students to justify their decisions.

Igneous rock Activity 5 Using igneous rocks Students create magazine adverts for items made from igneous rocks. They must make clear how the properties of the rock make it fit for purpose. Possible uses: granite – paving-stones, kerbstones, gravestones, kitchen worktops, flooring; basalt – flooring tiles, road-stone, railway ballast, cobblestones.