Environmental Engineering Reference
In-Depth Information
Rock Cycle
Before studying soil formation, it is important to understand how rocks are created and broken down on Earth.
The rock cycle is a continual process that breaks down, alters, and re-forms rock into one of three types. The
three types of rock are:
•
Igneous rock:
Igneous rock is formed from cooling magma. When magma cools slowly below Earth's
surface, it forms intrusive igneous rock, and when it cools quickly, as when ejected from a volcano, it
forms extrusive igneous rock. Examples of igneous rock include granite (intrusive) and basalt (extrus-
ive).
•
Sedimentary rock:
Sedimentary rock is the result of sediments derived from erosion and weathering be-
ing compressed and cemented together. Clastic sedimentary rock is formed after rock is physically
eroded, and chemical sedimentary rock is formed when dissolved minerals precipitate from water.
Examples of sedimentary rock include sandstone (clastic) and limestone (chemical).
•
Metamorphic rock:
Metamorphic rock is formed under extreme heat and pressure, usually deep under-
ground. When heat and pressure force minerals to align and create a layered formation, this is called fo-
liated rock. Unfoliated rock is not layered. Examples of metamorphic rock include marble (unfoliated)
and slate (foliated).
One type of rock can be converted into another type through Earth's continual geologic processes.
