Different Categories of Rocks (Third Grade Earth Science continued)
The second type of sedimentary rock is chemical, formed from chemical precipitation. When water passes through rocks and soil, it takes minerals along with it. Eventually, the minerals build up and the water evaporates, leaving behind all the minerals which join together to form a rock. The rock salt we use for cooking is formed this way!
Clastic rock is the third and final type of sedimentary rock. This is probably the most popular sedimentary rock because it's the type anyone can identify. Clastic sedimentary rocks are made up of pre‐existing rocks and bits of sand, silt, and clay. These materials become compacted together and form
one rock. Even though it's become one rock, you often can still see the bits of other rock either sticking out or embedded into the clastic rock face. You often find clastic sedimentary rocks by the beach.
Finally, we come to the third rock classification: metamorphic. This rock type is formed from the heating and application of high pressure to either igneous, sedimentary, or early forms of metamorphic rock. Combining heat (never high enough to melt the rock or else it will become igneous) and pressure causes the mineral structure within the starter rocks to change. The minerals morph and become a new rock.
Based on their structure, there are two types of metamorphic rock. The first type is foliated, this is when the pressure sort of stretches the rock making it look like sheets of stretched out rock. Sometimes you can see the striations in the stretches. The second type of metamorphic rock is non‐foliated. This is simply metamorphic rocks that do not have this sheet like structure. Usually metamorphic rocks that are non‐foliated occur when the original rock grains cannot align.
Now that you know the different types of rocks, you can fully understand the rock cycle! The rock cycle begins with a rock, any rock. This rock is beaten down through weathering and it erodes or breaks apart into pieces. The pieces then get deposited into various places within the earth. Some of these pieces will become compacted, turning into sedimentary rock and start the cycle again.
Other pieces become subjected to heat and pressure, changing their minerals and making them metamorphic rock, after which they start the cycle again. Yet other pieces do not end at the metamorphic stage. Rather more heat is added and the pieces melt and then undergo intrusive crystallization or extrusive cooling, forming igneous rocks which start the cycle all over again.
Next Article: Rock Reactions
