Secrets of Rocks:
The secrets hiding in rocks!
Rocks are actually made up of a mineral or mixture of minerals. They can also contain fossilized remains of plants and animals. The study of rocks is called petrology.
While rocks are not alive, of course, they still do have a " life cycle" of sorts. They are born as igneous rocks from hot molten rock called magma. When magma cools its elements combine to form minerals. Scientists have identified around 1,500 minerals so far. If the magma cools before it gets to the surface, it forms intrusive igneous rock. Granite is an example of this type of rock. If it cools outside of the crust it is called extrusive igneous rock. Basalt is an example in this category.
Sedimentary rocks have a family history, you could say, because they are kind-of like the children of the other rocks. They are formed from older rocks and rock formations. The weathering of these older rocks cause little pieces to break off and eventually break down to form the sand, soil, and mud. Water causes them to be carried into rivers, lakes and the sea. When they finally settle down, they start forming layers of rock called strata. Fossils are found in sedimentary rocks and we can learn alot about the earth's geological history from these layers of rocks.
Metamorphic rocks are a different story. They can be formed from both igneous and sedimentary rocks. The word is from the Greek word meaning "change of form", and that's exactly what happens. The powers that cause the change are: pressure and heat from the earth, water action, and the effect of hot magma on old rocks. The most common metamorphic rock is Gneiss.
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