In this week’s Homeschool Science Corner, we are going to look at the three main types of rocks – igneous, sedimentary, and metamorphic.
Each of these is composed of different minerals found in the Earth’s crust and core. We are also going to discuss crystals a bit, since they are made out of minerals as well.
This post is in no way meant to be an exhaustive look at this subject, rather it is meant to be a jumping off point for further studies on rocks. With that out of the way, I’ve got several activities and free printables for you too, so let’s get started.
Types of Rocks
So as I alluded to before, rocks are a solid mineral material that form the crust of our planet. In some places they are exposed to the surface, while in others, the soil covers this layer up.
Rocks can be broken into three main categories based on how they were formed. Those divisions are:
- Sedimentary rock – This type of rock is made from various layers of crushed minerals and the decayed remains of plants or animals. The layers can easily been seen and sedimentary rock tends to be very weak.
- Metamorphic rock – This type of rock that has been changed by heat or pressure. Metamorphic rock is very strong and the layers in it can be difficult to distinguish.
- Igneous rock – This type of rock is formed by fire. It begins as molten rock, or magma, from the Earth’s core and cools to form igneous rock. The shape and form is determined by how quickly it cools.
Crystals don’t fall into what we normally consider to be rocks, but they are composed from the same minerals. The difference is that these minerals were in high enough concentration and they had enough space to form the shape they were meant to be. This could have happened as the molten rock cooled or through deposits that form as water moves through the rock.
Sedimentary vs. Metamorphic Rock Activity
Ok, now that you know how to explain the different types of rocks to your students, let’s do a simple activity to help them see the difference between sedimentary and metamorphic rock.
You will need the following:
- Glass cup
- Chocolate chips
- Peanut butter chips
- Toffee chips
- Plastic wrap
Begin by adding ¼ cup of chocolate chips, followed by ¼ cup of peanut butter chips, and finally by ¼ cup of toffee chips. Repeat the layers once more before pressing down very gently with your hand. Observe how the layers look in the cup.
Next, use the spoon to press down and crush the layers as much as you can. Now, observe how the layers look in the cup. (The students should see that the layers are relatively compact, but still easy to define. This is meant to be a representation of sedimentary rock.)
Then, cover the cup with plastic wrap and heat it in the microwave at 45 second intervals until all the layers have melted together. (CAUTION: At this point the cup and the material will be extremely hot. Do NOT remove them until the cup has completely cooled.)
After the cup cools, take it out of the microwave. Observe how the layers in it look at this point. (The students should see that the layers are even more compact and it is very difficult to discern them. This is meant to be a representation of metamorphic rock.)
More to Explore
Here are several activities you can use to explore more about rocks:
- Make a Rock Collection – Have the students collect and identify rocks from around your home. Be sure to identify the rocks with their name and the type of rock they are. The students could also include information about mineral composition and where that particular rock is typically found.
- Grow your own Crystals – Have the students grown their own mineral crystals. Borax crystals are one of the easiest and most reliable crystals to grow at home. You can see how to grow these in this post on winter science fun.
I also have pinned several other rock-related activities on our Earth Science Pinterest Board.
Here are a few books you can use to explore more about rocks:
- Let’s Go Rock Collecting (Let’S-Read-And-Find… Science. Stage 2) by Roma Gans and Holly Keller
- Rocks: Hard, Soft, Smooth, and Rough (Amazing Science) by Natalie M. Rosinsky and Matthew John
- The Rock Factory: The Story About the Rock Cycle (Science Works) by Jacqui Bailey and Matthew Lilly
- The Rock Cycle (Earth Science) by Melanie Ostopowich
- National Geographic Readers: Rocks and Minerals by Zoehfeld, Kathleen Weidner
I trust that this post will help you explain to your students about the different types of rocks!