Rocks are naturally occurring objects that are made up of minerals. Many rocks are parts that have fallen off of mountains or they came from a cave. There are rarely rocks that are completely identical to each other. They may have come from the same source, but the process that created them makes them unique, which is why there are many rock collectors and enthusiasts out there. The forming process of rocks is what separates them into three categories: igneous, sedimentary, and metamorphic.

Igneous

They are often called fire rocks because they are formed from magma hardening and cooling in a volcano or after it erupts. The proper term for magma above ground is called lava, so igneous rocks form from cooled and hardened magma or lava. Magma and lava do not cool down in the same way, which is why igneous rocks look so different from each other. As lava cools, the rocks form with crystals, which form extrusive rocks that are shiny, like basalt.

Sedimentary

Sedimentary rocks are found at the bottoms of lakes, oceans, and rivers due to the erosion of Earth’s surface due to wind and water. The rocks are formed from the bottom layers of eroded Earth being pressed down upon, or by the organic material being cemented together by the water. These rocks will often contain fossils; will vary greatly in size; and will have visible layers. Sandstone, limestone, and shale are some examples of sedimentary rocks.

Metamorphic

Over time, igneous and sedimentary rocks will change and eventually will become metamorphic rocks. This is due to the immense pressure and heat from magma under the Earth’s surface. If a rock is heated long enough at a high enough temperature, it will transform into a different type of rock. When the layers of igneous and sedimentary rocks and other organic materials press down on each other, the very bottom layer cannot handle all of the weight and pressure after a while and will therefore change into a metamorphic rock. Sandstone will become quartzite, shale becomes slate, and limestone becomes marble.

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This entry was posted on Friday, October 28th, 2011 at 7:55 pm and is filed under Types of Rocks. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.