What is a rock?

To geologists, a rock is a natural substance composed of solid crystals of different minerals that have been fused together into a solid lump. The minerals may or may not have been formed at the same time. What matters is that natural processes glued them all together.
There are three basic types of rock: igneous, sedimentary, and metamorphic.

Extremely common in the Earth's crust, IGNEOUS ROCKS are volcanic and form from molten material. They include not only lava spewed from volcanoes, but also rocks like granite, which are formed by magma that solidifies far underground.

YOU CAN TAKE PICTURES OF IGNEOUS ROCKS FROM FOLLOWING LINKS

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http://www.mineralogy4kids.org/sites/default/files/granite_0.jpg

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Sedimentary rocks are formed from eroded fragments of other rocks or even from the remains of plants or animals. The fragments accumulate in low-lying areas—lakes, oceans, and deserts—and then are compressed back into rock by the weight of overlying materials. Sandstone is formed from sand, mudstone from mud, and limestone from seashells, diatoms, or bonelike minerals precipitating out of calcium-rich water.

YOU CAN TAKE PICTURES OF SEDIMENTARY ROCKS FROM FOLLOWING LINKS

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Metamorphic rocks are sedimentary or igneous rocks that have been transformed by pressure, heat, or the intrusion of fluids. The heat may come from nearby magma or hot water intruding via hot springs. It can also come from subduction, when tectonic forces draw rocks deep beneath the Earth's surface.

YOU CAN TAKE PICTURES OF METAMORPHIC ROCKS FROM FOLLOWING LINKS


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http://www.mineralogy4kids.org/sites/default/files/quartzite_0.jpg

http://www.mineralogy4kids.org/sites/default/files/phyllite_0.jpg