Gene Uhi
Geology 1010
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Rock Cycles
Rocks are the building blocks of everything we have come to use, from homes to medical
supplies; but for these innovations to be possible we must first find out how these materials are formed.
In the following paragraphs I will explain how each rock types are formed. The very beginning of a rock's
life cycle starts with great pressure and/or heat.
Igneous rock is solidification of lava or magma. There are two different ways that igneous rocks
are formed. Intrusive is an igneous rock that is formed by the solidification of magma, and is also known
as Plutonic Rock. Extrusive or Volcanic Rock is an igneous rock that is formed by the solidification of lava.
Everything on the Earth’s surface experiences various types of weathering which lead to the next major
occurrence in rock development.
After the Igneous rock has solidified on the Earth’s surface it is attacked by either form of
weathering, mechanical or chemical. Mechanical weathering is a process which breaks a rock up into
smaller pieces but does not change the chemical makeup. Chemical weathering is a process which
breaks a rock into smaller pieces and changes the chemical makeup. Both weathering types play a key
role for the next step of the rock cycle.
Sedimentary rocks are loose rocks that have been compacted into a more solid larger rock. You
may wonder how these little pieces are put back together to create a new rock. Cementation,
Compaction, and Recrystalization is how small unconsolidated rock material is combine together to
make a rock. Cementation is when minerals that have been chemically dissolved in water, begin to
collect back into the small rocks. Compaction is where the weight of an object above is pressing down
onto small rocks forcing them to fuse together. Salt crystals begin to grow as water evaporates. There
are three different types of sedimentary rocks Detrital Sedimentary Rocks, Chemical Sedimentary Rocks
and Organic Sedimentary Rocks. Detrital Sedimentary rocks are fragments of pre-existing Rocks.
Chemical Sedimentary Rocks are minerals that have been dissolved in water then as it drips the minerals
are left behind. Organic Sedimentary Rocks is when organic material changed into rocks. You may be
wondering what would happen if a sedimentary rock is partially melted or mixed into something else
entirely?
Metamorphic rocks are rocks that have been changed by a combination of heat, pressure and or
chemicals. On plate boundaries you have one plate being thrust underneath another (Oceanic Crust or
Continental Crust) or the colliding together and crumpling; these are examples of convergent plate
boundaries. When Continental Crust collides with each other they create a mountain range, the top half
of the mountain range will be the crust and the lower half will be metamorphic rocks. Now if it is
Continental Crust and oceanic crust, the Oceanic Crust will be pushed down into the mantle of the Earth.
The Point of collision is where there will be metamorphic rocks. If Oceanic Crust and oceanic crust
collide the heavier of the two will sink into the mantle and the point of impact will be where the
metamorphic rock is.
There are two different types of metamorphic rocks, foliated metamorphic rocks and nonfoliated metamorphic rocks. Foliated metamorphic rocks are preferred orientation and or preferred
distribution of the mineral crystals in a metamorphic rock. Preferred orientation is where the crystals
are all pointing the same direction. Preferred distribution is where the crystals are spaced apart
precisely. Preferred orientation and distribution is where the crystals are spaced precisely and pointed
in the same direction. Non-foliated Metamorphic Rocks are the complete opposite of Foliated
metamorphic rocks; they are more chaotic in their preferred orientation and distribution.
After igneous rocks are formed they can take one of two roads, one is weathering and the other
is changing into a metamorphic rock but for now let’s say that it undergoes weathering and changes.
Once weathering has occurred on the igneous rock it will change into sediments. Then the lithification
process begins and changes the sediments into Sedimentary Rocks. After Sedimentary Rocks have
formed it can take one of two roads it can go back and be re-weathered or go forward and be changed
into a metamorphic rock. Once the metamorphic rock has finished it can take one of three roads, go to
the beginning and be changed into a sedimentary rock or go back and go through metamorphism again
or go forward be cooked to melting point and start the whole process all over again, which is called the
Rock Cycle. The rock cycle is a vast cycle which repeats. Below is the full rock cycle.