D. Crowley, 2008

 To know how igneous rocks are formed, and how this affects their appearance

 Look at the examples of some igneous rocks  What similarities do they have?  What differences do they have?  Do they have crystals / layers / fossils / grains etc… Gabbro Granite Basalt Pumice

Granite Pumice Basalt Obsidian Rhyolite Andesite

 Igneous rocks are one of the three main groups of rock classification (along with sedimentary and metamorphic)  They are formed within the Earth (where temp. is hot enough to melt rock)  Molten (liquid) rock forms when rocks melt, called magma  When the magma cools and solidifies igneous rocks are formed

 We live on the Earth’s crust, and underneath this is a layer called the mantle  The mantle and the crust can melt as the Earth is extremely hot - the molten rock is called magma  When magma cools it can form igneous rocks  Magma which reaches the Earth’s surface is called lava

 Igneous rocks contain interlocking crystals which are held together very strongly and make the rock hard  The crystals in igneous rocks have a disorderly arrangement  Igneous rocks never contain fossils (as the rock has been melted, destroying the fossils)  The size of the crystals depends on how quickly the igneous rock solidifies…

 Igneous rocks are formed when magma cools and solidifies  When magma cools above the surface, extrusive igneous rocks are formed  When magma cools below the surface, intrusive igneous rocks are formed  Their crystals vary in size depending upon how quickly the magma cools…

 Igneous rock crystals vary in size, depending on how quickly the molten rock cools  Carry out the salol experiment – place the salol on a hot slide / cold slide and observe the difference in crystal size… Cooled rapidly – small crystalsCooled slowly– large crystals

 How can we explain how the crystal size varies due to how quickly the rock cools?  When the rock is a liquid the particles are free to move about - as the molten rock cools, bonds form between the particles, sticking the particles together affecting crystal size… BasaltGranite Rapidly cooled (small crystals) Slowly cooled (large crystals)

 If the rock cools slowly there is time for lots of particles to move and stick together (bond) = large crystals  If the rock cools quickly only a few particles can move and stick (bond) together = small particles LARGE crystals small crystals

 Complete the changing Earth worksheet

Lava quickly igneous small Volcano Magma slowlyigneous largeMantle