Igneous rocks come in many different types, however the one thing they all have in common is that they are formed directly from cooling magma underground or lava if it surfaces. Igneous rocks:
- are hard and strong because of their mineral content
- resemble a jigsaw puzzle and are made of interlocking crystals that grow into each other.
The 3 main differences that can change are:
- If the rock is intrusive (formed underground) it will have large crystals from cooling slowly over time (right side of image). Or extrusive (formed above ground) which has many small crystals and looks more uniform in it’s make up.
- The silica content, which is a type of mineral found in rocks
- Extrusive rock can also be impacted on how much air is present during formation which may cause air bubbles.
- (see image below to compare the impact of these differences)
Uses of igneous rocks activity
Below are listed some of the uses of igneous rocks. Make a new word document or PowerPoint on your computer. Try to find some images and list the properties of the rocks that make them suitable for the use. e.g. granite has large coarse crystals which allow it to bear a lot of weight and it can also be polished smooth to make it look good.
To complete this task you should:
- have at least one image of each type of rock listed
- describe in your own words what it looks like
- discuss 2 key features as to why it is used for that purpose
| Basalt | Buildings, concrete (crushed rock), floor tiles |
| Dolerite | Road surfaces (blue metal), concrete (crushed rock) |
| Granite | Buildings, monuments, road surfaces, kitchen benchtops |
| Scoria | Landscaping, filters and concrete (crushed rock), barbecue rocks (to soak up fat). |
| Pumice | Cleaning dead skin off feet, emery boards, for shaping nails, some soaps that feel rough on your skin |
| Obsidian | Scalpel blade for surgery, ornaments and jewellery, Ancient weapons for cutting, spear and arrow points, and pots and vases. |
Mr Danic 