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A ROCK is any naturally formed solid in the crust made up of one or more kinds of minerals. Each mineral in a rock has its own streak, hardness or crystal shape. The most exact way to identify a rock is to name the minerals it contains. Rocks are grouped into 3 types according to how they were formed.
IGNEOUS ROCKS form when melted rock material cools and hardens.
Examples of igneous rocks- Rhyolite, Obsidian, Basalt, Granite and Gabbro.
Molten rock material deep below the surface is called Magma. Often magma makes it to the surface before hardening and it is called Lava.
SEDIMENTARY ROCKS are made up of small bits of matter joined together. Most common sedimentary rocks are formed when sediment is compacted or cemented together. Some are made of crystal of minerals that were once dissolved in water.
Examples of sedimentary rocks- Shale, Siltstone, Sandstone, Limestone and Coal.
Sedimentary rocks are useful in helping piece together Earth's history.
Limestone is used for buildings, trim, monuments, and even park benches.
Shale is often broken into pieces that are mixed with other materials to make concrete and cement.
Coal is a source of energy.
METAMORPHIC ROCKS are rocks that are formed under heat and pressure but remain solid. The mineral grains in the original rock may flatten and line up. The minerals may change their identity. The minerals in the original rock may separate into layers of different densities. In each case, the result is a rock different from the original.
ORIGINAL ROCK METAMORPHIC
The main ingredient in soil is weathered rock. Soil may also contain water, air, bacteria and humus. Humus is decayed plant and animal material.
Where does soil come from? A layer of solid rock weathers into chunks. The chunks weather into smaller pieces. Living things die and decay and form humus.
People depend on soil but at times ruin and waste it. People often get rid of garbage - Hazardous wastes, spraying chemicals, tossing plastics and foam remains, by burying them in the soil. All these materials add up to pollution. Pollution means adding harmful substances to Earth's land.
We can protect soil by:
1-Adding fertilizers and humus-add these materials to replace minerals
2-Using crop rotation-each year grow different crops to replace minerals
3-Strip farming-strips of tightly grown grasses are grown and trap runoff
4-Contour plowing-plow furrows across rather than up and down
5-Terracing-a hillside is shaped into a series of steps, runoff and eroded soil is trapped
Rocks are constantly changing from one rock to another. This process is called the Rock Cycle. Part of this cycle is the weathering of rocks into bits and pieces- some of which may eventually become soil. Rocks are a non-renewable resource.