LECTURE  2                                                                             THE ROCK CYCLE
THE ELEMENTS
The most common elements in the earth are oxygen, carbon, iron, nitrogen, silicon, and magnesium. 
- 90% of earth is iron (33.3%), oxygen (29.8%), silicon (15.6%), and magnesium (13.9%).

  Most iron (33.3%) is in the core 
magnesium (13.9%) is in the mantle

oxygen (46.6%) andsilicon (27.7%), compose almost 75% of the mass of the crust.  aluminum (8.1%), iron (5%), calcium (3.6%), sodium (2.8%), potassium (2.6%), magnesium (2.1%), and all others (1.4%).

MINERALS MADE FROM ELEMENTS

A MINERAL: 

1. is naturally occurring
2. made of inorganic materials
3. has a definite chemical compound
4. has a definite crystalline structure

MINERALS ARE CLASSIFIED AS:
A. silicates (SiO4=)
silicon and oxygen
B. nonsilicates
carbonate (CO3=)
oxide (O=)
phosphate (PO4=)
sulfate (SO4=)
sulfide (S=)
halide (F-, Cl-, Br-, I-)
gold, silver, copper, carbon (diamond or graphite), and sulfur.

HOW MINERALS ARE FORMED

A.  Mineral crystals form by precipitation from a water solution
( http://www.youtube.com/watch?v=Jd9C40Svt5g) http://www.youtube.com/watch?v=DpiUZI_3o8s&feature=related

 
 
 
 
 

 

B. Mineral crystals form by precipitation when cooling in molten magma

-- size of the crystals depends on the rate at which they form
-- slow cooling = large crystals, time for minerals to separate and come together .
.
-- fast cooling = small crystal 

-- Extremely rapid cooling  =  GLASS or obsidian, pumice or typical lava rock.

ROCKS are aggregates or mixtures of various MINERALS "cemented" together. 
Rocks are classified into three groups: 
IGNEOUS rocks are created by the cooling of magma. There are two main kinds of igneous rocks:

A.  granites
B.  basalts

- Granites make up much of the continents and are commonly used for buildings and monuments.  They are lighter and tend to ride up at subduction zones avoiding being recycled. This is one reason continents have gotten larger over time.

- Basalts are heavy and dense and form the ocean basins

- Basalts and granites are both very firmly cemented and strong

SEDIMENTARY rocks

- are  formed by deposition of eroded rock
- the kind of sediment depends on the kind of rock that was deposited
The layered walls of the Grand Canyon are sedimentary
The White Cliffs of Dover are sedimentary limestone (chalk) deposit formed largely from the shells of marine animals.

- limestone (from carbonates, shells)

- shale (from aluminum oxides or clay)

- sandstone (from sand, silicates)

- These are the softest type of rocks

METAMORPHIC rocks

- are partially remelted igneous or sedimentary rocks

- Marble formed from limestone 
(carbonate) deposits

- Slate formed from shale 
(clays, aluminum oxides) deposits

- Quartz from sandstone
(silicates aka sands) deposits

- These are intermediate in strength, harder than sedimentary, softer than igneous

limestone
marble
shale
slate
sandstone
quartz
The oldest known rocks are about 3.8 billion years old
found in Greenland, northeastern Canada, and Australia and are metamorphosed granites.

 
The change from one type of rock into another is called the ROCK CYCLE. 

   WEATHERING and EROSION 
WEATHERING

  is when large chunks of rock is broken into smaller pieces
mechanism is weather, chemical, and biological processes.
 
Water - ice is most common and has the biggest impact on rock through freeze thaw cycles (potholes in spring) 
(http://www.youtube.com/watch?v=U7L1W1RaLZw&feature=related)
Chemical the minerals in rocks reacts with oxygen, carbonic acid (H2CO3) and water.
- acidic waters will dissolve some minerals which weakens the structure of the rock (rotten granite)
- it is what causes limestone caves such as Mammoth Cave in Kentucky or Carlsbad Caverns in New Mexico
- acid waters drip, drip, drip thru the limestone dissolving minerals which redeposit on the inside of the cave walls, ceilings and floors.
Biological the greatest is tree roots which can split the rock right off a cliff, especially in combination with expanding ice
- however, caves have now been show to be eaten away by certain bacteria that make sulfuric acid that dissolves various minerals 

 

EROSION

  is the movement of rocks and soil by water, glaciers, by wind, and by gravity
 
Earth flows and mud slides occur when the soil is saturated with water (California)
Streams and rivers carry large quantities of sediment that are eventually deposited in the entrance to oceans called deltas.  (New Orleans)
Glaciers can move rock fragments up to the size of large boulders.  The moving ice and rock further scrapes gouges the sides and bottom of the glacial valley.  If the end of the glacier occurs on land, the melting ice deposits large quantities of rock fragments to form a moraine. (Wisconsin)
- The last ice age ended about 11,000 years ago.  Glaciers covered much of North America, Europe, and Asia,  including most of Wisconsin.
 Wind can weather rock by sandblasting it with flying grit and erode rock by picking up small fragments and blowing them away.  When wind blows across dry soil not protected by vegetation huge quantities of soil are blown away.  The "Dust Bowl" of the 1930s was an episode of this sort. 
Material carried by the wind is deposited as sand dunes or as extensive areas of fine dust called loess.  Loess has an open porous structure that holds water and it usually contains materials needed as plant nutrients making it a fertile soil.  There are extensive loess deposits in the central United States.

THE FORMATION OF SOIL
SOILS are a mixture of 
1. small rock fragments (really tiny, sand and clay)
2. organic material 

Knowing And Building Your Soil this article must be read

Review:

What are MINERALS?
Why do elements combine to form minerals?
Discuss the different ways crystals are formed, what conditions favor small or large crystals?
What happens when magma is cooled extremely fast?
How are obsidian, pumice or typical lava rock formed?  Why do they look so different?
What are rocks?
Discuss the 3 classification of rocks, how they are formed and give an example of each.
How is marble formed?
How is shale formed?
How is quartz formed?
How old are the oldest rocks and what kind are they?
What is the "rock cycle"?
What is "soil", how is it different from minerals and rocks?
How is "Weathering" different from erosion?
Discuss the main forces that weather rock.
Discuss the main forces that cause erosion of rock.
What causes Earth flows and mudslides? Where is this more likely to occur?
What is Loess?