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Earth Science- Lecture 3


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Earth processes and properties of rocks?
Any Earth process that happens around us is closely related to the properties of rocks. Volcanic eruption, orogenisis (mountain building), weathering, erosion, and earthquakes.
Rocks carry clues...
About the environment they formed; fossils, size of minerals and particles that make up the rocks may give us info about where they came from.
Based on origin...
Divide rocks into 3 groups:

Concept of the rock cycle
Outlines of physical geology.

Starts with molten rock called magma.
Cools and solidifies beneath the the surface of the earth. Called crystalization.
Igneous Rocks...
Formed from magma.

Igneus rocks will start to disintegrate and slowly decompose, or weather, due to atmospheric influences.
Decomposed Rocks?
Called sediment, can be transported by winds, glaciers, rivers, and/or waves to the bottom of the oceans or lates.

Slowly turn to rocks through lithification.
Takes place when sediments get compacted by overlaying layers and get cemented by minerals carried by the water. The resulted rocks are sedimentary.
Sedimentary Rock?
When it is buried deep within the earth or went through the process of mountain building, it will be subjected to pressure and heat.

Causes sedimentary rock to turn to metamorphic rock.
Metamorphic Rock?
When influenced by higher pressure and heat it will melt and become a molten rock called magma. The cycle continues.
Cycle can have shortcuts...
Sometimes, igneous rocks will encounter high pressure and heat and form metamorphic rocks and metamorphic rocks will then undergo weathering to form sedimentary rocks.
Magma originates...
At depth as great as 200 km or 120 miles. Consists of silicon, O2, Aluminum, Iron, Calcium, Magnesium, Potassium, Sodium, water vapor, and gases.
Volcanic Eruption?
Whenever magma breaks to the surface it produces a volcanic eruption. Great explosions occur when the gases escape due to lessening pressure near the surface.

During these, rock fragment ejections and lava flows also take place.
2 kinds of magmatic rocks?
Extrusive/Volcanic- magma reaches the surface and solidifies.

Intrusive/platonic- magma cannot reach the surface and solidifies at depth.
The ions within the magma move freely as magma cools, the movements of the ions slow and arrange themselves into orderly fashions forming crystals. When no space is left, the crystal growth stops.
Slow cooling?
Results in large crystals.
Rapid cooling?
Results in small crystals and ions lose their motion and quickly combine. This results in tiny crystals.
Instantaneous cooling?
Not sufficient time for ions to come together into arranged patterns but rather, they produce a solid, randomly arranged ion like glass.
How are igneous rocks classified?
By their texture and mineral composition.
4 parts of texture?
Coarse grained
Fine grained
Overall appearance of an igneous rock based on the size and arrangement of interlocking crystals.
Fine grained texture?
Tells us that igneous rock has formed rapidly at the surface and crystals can be seen with the aid of a microscope.

Some rocks formed like this have voids that are created by escaped gases.
Coarse grained texture?
Tells us that iugneous rocks that have formed slowly have larger interlocking crystals that can be seen without a microscope.
Porphyritic Texture?
Crystalization rate of materials in magma is different. Some are large, some still need time to grow. If magma like this suddenly erupts at the surface, the remaining magma occurs rapidly. The resulting rock has appearance of large crystals embedded in smaller ones.
Glassy Texture?
Due to volcanic explosion, rapid cooling occurs and ions do not have enough time to arrange themselves into an orderly structure, creating a glassy texture.
Also created in a glassy process. But has lots of voids due to escaped gases during eruption.
Mineral Composition?
Certain Minerals?
Will crystalize at certain temperatures at certain depths. Heavier elements will crystalize first.
Cooling at different temperatures?
Affects the texture.
Chemical components of magma?
Will effect the mineral composition
Weathering of rocks?
Disintegration of rocks due to a natural process.

Natural response of Earth materials to a new environment.
Two kinds of weathering?
Mechanical and chemical.
Physical weathering of rocks (breaking into pieces) result products are STILL THE SAME.
3 ways of mechanical weathering?
Frost wedging, unloading, biological.
Frost Wedging?
Alternate freezing and thawing of water expands 9% when it freezes and creates a big, outward force.
Exposed igneous rocks break layer by layer due to erosion. Called sheeting.

Unloading causes great pressure reduction and outer layer expands and separates from the rest of the rock (granite)
Plant roots- organisms- burrowing animals in search of water- grow into fractures and disintegrates the rocks into smaller pieces.
Altering the internal structure of minerals (removing or adding elements) Result product has changed but is stable. Water is the most important agent. Rain and air from weak H2C03
As this acid reacts with granite minerals quartz and potassium feldspars. Potassium ions are displayed- mineral's chemical structure changes. Potassium feldspar produces "clay". Leftover minerals are carried by water, making sandy beaches or settling to produce.
Sedimentary rocks are vital to geologists...
Holds info regarding the history of Earth and geological environment.

- Fossils
- Size of Grains
- Thickness of strates (layers)
- Colors of layers
- Ripple marks
Sedimentary rocks are economically vital...
to petroleum, coal, ore, sand, gravel, etc.
Fossils and Oil?
Only found in sedimentary rocks. Too much heat to find elsewhere.

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