A rock is a solid made up of a bunch of different minerals. Rocks are generally not uniform or made up of exact structures that can be described by scientific formulas. Scientists generally classify rocks by how they were made or formed.
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Three Major Types of Rocks
Metamorphic Rocks – Metamorphic rocks are formed by great heat and pressure. They are generally found in the Earth’s crust where there is enough heat and to form the rocks. Metamorphic rocks are often made from other types of rock. A sedimentary rock can be changed, or metamorphosed, into a metamorphic rocks such as slate or gneiss. Metamorphic rocks include marble, anthracite, soapstone, and schist.
Igneous Rocks – Igneous rocks are formed by volcanoes. When a volcano erupts, it spews out hot molten rock called magma or lava. Eventually, the magma will cool down and harden, either when it reaches the Earth’s surface or somewhere within the crust. This hardened magma or lava are called igneous rocks. Igneous rocks include basalt and granite.
Sedimentary Rocks – Sedimentary rocks are formed by years and years of sediment compacting together and becoming hard. Generally, something like a stream or river will carry lots of small pieces of rocks and minerals to a larger body of water. These pieces will settle at the bottom and over a really long time (perhaps millions of years), they will form into solid rocks. Sedimentary rocks are shale, limestone, and sandstone.
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The Rock Cycle
Rocks are constantly changing in what is called the rock cycle. It takes millions of years for rocks to change.
1. Melted rocks or magma is sent to the earth‘s surface by a volcano. It cools and forms an igneous rocks.
2. Next the weather, or a river, and other events will slowly break up this rocks into small pieces of sediment.
3. As sediment builds up and hardens over years, a sedimentary rock is formed.
4. Slowly this sediment rocks will get covered with other rocks and end up deep in the Earth’s crust.
5. When the pressure and heat get high enough, the sedimentary rock will metamorphose into a metamorphic rock and the cycle will start over again.
There are actually some rocks that come from space called meteorites. They may have different elements or mineral make up than a typical earth rock. Typically they are made up mostly of iron.
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Interesting Facts about Rocks
- The word “igneous” comes from the Latin word “ignis” which means “of fire.”
- Ores are rocks that include minerals that have important elements such as metals like gold and silver.
- Sedimentary rocks form layers at the bottoms of oceans and lakes.
- Marble is a metamorphic rocks formed when limestone is exposed to high heat and pressure within the Earth.
- Layers of sedimentary rocks are called strata.