Rocks are all around us. You can see rocks inside your house, in your yard, on your street, on a country road, everywhere you look. Statues, chalk, marble, pencil lead, sandpaper, glass, tombstones, bricks, the walls of your room, mountains, pebbles, soil, and volcanoes are all rocks!!
Humans have used the metals and minerals in rock since the beginning of civilization. Rocks are used to build homes, an aluminum baseball bat, a washing machine, video games, airplanes, cars, and jewelry! Rocks aren't always solid. Sand and mud are rocks. No matter where you are, you are always close to rocks and minerals. They are fascinating and exciting, so let's begin our investigation to learn more.
Let's start at the beginning …
We'll begin with a look at the structure of the earth because that is where all rocks come from. They have been on Earth for almost 4 billion years. Geologists record time with the Geologic Time Table.
Where do rocks come from?
The Earth has 3 layers: the crust, the mantle and the core (which is subdivided into the outer and inner core). Each layer is unique. You can find the interesting details about the layers at The Structure of the Earth.
How do we classify rocks?
There are 3 main types of rocks depending upon how they were formed in the different layers of the Earth. They are: Igneous, Sedimentary, and Metamorphic.
Metamorphic rock forms when igneous, sedimentary, or other metamorphic rock is changed by heat and pressure.
This type of rock is buried deep within the Earth where it is created from the heat and pressure found there.
Is hard, often contains crystals, and may have bands or layers.
Examples: marble, slate, gneiss, schist
Perhaps this little “rock” song will help you remember the differences among sedimentary, igneous, and metamorphic rocks. Sing it to the tune of “Row, Row, Row Your Boat.”
Sedimentary rock has been formed in layers
Often found near water sources with fossils from 'decayers.'
Then there's igneous rock, here since earth was born.
Molten lava cooled and hardened that's how it is formed.
These two types of rock can also be transformed
With pressure heat and chemicals, met - a - morphic they become.
Rock On! By Cherry Carl
Rocks! Rocks! They're not the same!
Each one has its claim to fame.
Rocks are grouped in three main types:
Some have layers … some have stripes.
What makes them different, do you know?
Let's take a look at rocks on show.
This rock star is “igneous.”
It's made when earth seems furious.
Liquid rock erupts and cools,
Forming solid glasslike pools.
“Metamorphic” means some changes.
Mother Nature rearranges.
Using heat and pressure, too,
She makes old rocks appear as new.
“Sedimentary” means small pieces
That nature generally releases.
Using wind and water, too,
It makes new rocks for me and you.
Rocks! Rocks! You're not the same!
It's easy now to know your name.
Cherry Carl wrote this poem especially for Science Trek. For additional poems on science, history, language, and holidays, visit her website at Carl's Corner.
A rock can begin as one type and can change many times. In fact, rocks are always changing. However, the changes happen so slowly that they are difficult to see. We have seen above that heat and pressure can change rocks, which then break down by weathering and move by erosion. It can take thousands of years for rocks to weather and erode. This process of change is called the rock cycle.
Weathering is the process that breaks rocks down into smaller pieces. Weathering can be caused by wind, rain, ice, running water, plant roots, chemicals, freezing and thawing.
Erosion is the movement of rock pieces from place to place. Erosion can be caused by wind, rain, running water, waves, gravity, and moving ice.
The heads at Mt. Rushmore are carved out of an igneous rock called granite.
The heat from lightning striking beach sand can melt the sand to form a glassy rock called “fulgurite.”
Melted rock is called magma when it is inside the earth, but called lava when it runs out onto the surface of the earth.
The mineral, salt, was so valuable in ancient times that it was traded ounce for ounce for gold.
A diamond is the hardest mineral.
Meteorites are rocks from space, and they can help scientists learn about the solar system.
What else do we know about rocks?
A rock is a material made of one or more minerals. Minerals are made from 92 elements that join together in many different ways. Some minerals are made of only one element, such as silver, but most are a combination of two or more elements. For example, the mineral quartz is made of the elements silicon and oxygen. The rock we know as granite is contains the minerals quartz, feldspar and mica. So, rocks are composed of one or more minerals, and minerals are composed of one or more elements.
Scientists have identified over 3,000 minerals. When the mineral particles are arranged in a repeating pattern, they are called a crystal.
Recognizing a mineral is not an easy job. There are several different properties of minerals and tests that are used to identify them. The properties include luster, hardness, color, streak, cleavage, crystal shape, and magnetism. You can view descriptions of these properties.
Want to learn more about the rock cycle?
The rock cycle is complex but you can learn a lot by revisiting the idea of it over and over. Check out these sites for more information: