1. Chapter 6: Rocks

2. Section 1: Rocks and the Rock Cycle
 What are rocks?
Rocks can be a collection of one or more minerals or rock can be made of solid organic matter.
What do geologists study?
Geologists study the forces and processes that form and change the rocks of the Earth’s crust.

3. Three main types of Rocks
What does igneous rock mean?
It means “from fire”
How is igneous rock formed?
When magma or molten rock cools and hardens.
* Magma is called lava when it is exposed to Earth’s surface.

4. Sedimentary Rocks What are sediments?
Sediments are rocks, mineral crystals and organic matter that have been broken into fragments.
How are sedimentary rock formed?
When the sediments are compressed, cemented together and hardened.

5. Metamorphic Rocks
What is metamorphic rock? It is rocks that have gone through tremendous pressure, extreme heat and chemical processes that change the existing form of the rock.

6. The Rock Cycle
What is the Rock cycle? The process when any of the three types of rock that can be changed into another. Properties of Rock All rock has physical and chemical properties that are determined by how and where the rock was formed.

7. Bowen’s Reaction Series
In the 1900’s a Canadian geologist studied how minerals crystalized from magma. *He learned that as magma cools certain minerals crystalize first. * Different minerals form at different times during the solidification (cooling) of magma

8. Chemical Stability of Minerals
Is a measure of the tendency of a chemical compound to maintain its original chemical composition, rather than break down to form a different chemical.
When are minerals most stable?
When they are formed at the lowest temperatures.

9. Physical Stability of Rocks
Rocks have natural zones of weaknesses that are determined by how and where the rocks form.
Sedimentary and metamorphic rocks tend to break down around the layers.
What are joints?
When igneous rocks have evenly spaced zones of weakness.

10. Section 2: Igneous rocks

11.  How does magma form? It forms when rocks melt.
The chemical composition of minerals determine their melting point.
The addition of fluids decreases the melting point of certain rocks.

12.  What is partial melting?
The process by which different minerals in rock melt at different temperatures.

13.  Fractional Crystallization
The process of removal of different minerals from the cooling magma
The largest crystals are the ones that formed the earliest because they have a longer cooling time.

14.  What is the difference between extrusive and intrusive rock?
Intrusive igneous rock is formed inside the crust. These enter into other rock masses beneath the Earth’s crust.
Extrusive igneous rock is lava that cools at the Earth’s surface.
Both differ where they form as well as the size of the crystals or grains.

15.  Coarse-Grained Igneous Rocks
These have large mineral crystals and are typically intrusive.
Ex. Granite.

16.  Fine-Grained Igneous Rocks
Small mineral grains that can not be seen by the eye.
Mostly extrusive.
Example basalt and rhyolite

17.  Other Igneous Rocks
Porphyritic texture – form large and small crystals
Ex. Granite
Glassy – magma cools quickly, few crystals grow and the rock looks shiny.
Ex. Obsidian
Vesicular texture - rapidly cools with holes in it.
Ex. Pumice

18.  What are the three types of igneous rocks?
Felsic, Mafic and intermediate
The mineral composition is determined by where the rocks are formed.

19.  What are some examples of felsic rock?
Granite, rhyolite and pumice
These rocks are created from magma that have a large quantity of silica. These rocks are mostly light colors.

20.  What are some examples of mafic rock?
Basalt and gabbro
These rocks are rich in iron and magnesium. They have significantly less silica than felsic rock.
These are typically a dark color.

21.  What are some examples of intermediate rock?
Diorite and andesite
These rocks have a middle amount of silica compared to mafic and felsic rocks.

22.  Intrusive Igneous Rocks
Largest type is batholiths
Laccoliths push the ground up and form small dome-shaped mountains.
Sills lie parallel to existing rock layers
Dikes cut across the rock layers. These are common in areas with volcanic layers.

23.  Extrusive Igneous Rocks
Volcano is a vent which magma, gases or volcanic ash is expelled.
Lava flows are flat masses of rock.
Lava plateaus – cover a vast area with thick rock
Tuff forms when volcanoes release ash during an eruption. It can cover several hundred kilometers.

24. Section 3: Sedimentary Rocks

25.  What are sediments?
Sediments are loose fragments of rock, minerals and organic material that result from natural processes including the physical breakdown of rocks.
After sediments form they are transported by wind, water or ice to new locations.

26.  Describe compaction and cementation
Compaction is the process in which sediments are squeezed and the pore space is reduced by pressure.
Cementation is the process in which sediments are glued together by minerals that are deposited by water.

27.  What are the three main types of sedimentary rock?
Chemical, organic and clastic

28.  Chemical Sedimentary Rock
Form when ions from dissolved minerals precipitate out of water because of changing concentration in chemicals.

29.  Organic Sedimentary Rock
Is rock that forms from the remains of living things.
Coal forms from plant remains that are buried before they decay and are then compacted into matter that is completed composed of carbon.
Organic limestone comes from coral, clams, oysters and plankton that remove chemicals from the water to make their shells,. When they die the shells eventually become limestone.

30.  What is a clastic sedimentary rock?
Rocks that are caused by fragments of pre-existing rocks that are cemented and compacted together.
Conglomerate – composed of rounded fragments that range in size from 2 mm to boulders
Breccia – fragments are angular and have sharp corners
Sandstones – made up of sand-sized grains cemented together
Shale – consists of clay-sized particles that cemented and compacted together. The clay particles are typically pressed into flat layers.

31.  Characteristics of Clastic Rock
Sediments are transported by water, ice, wind and the effects of gravity.
The size and the speed the sediments travel impacts have far the sediments will move.

32.  Sorting
The tendency for currents of air or water to separate sediments according to size is called sorting.
When well sorted all of the sediment grains are the same size and shape.
In poor sorted sediments the grains are many different sizes.

33.  Angularity
As particles first break down they are rough but over time they are smoothed away.

34.  What is depositional environment?
It is where the sediments are deposited such as rivers, deltas, beaches and oceans.

35.  What is stratification?
Stratification is layering of sedimentary rocks
Beds are layers that vary in size.
Massive beds are beds that have no internal structure.

36.  What are cross-beds and graded bedding?
Cross beds are slanting layers
Grading bedding – different sizes and shapes of sediments settle to form different layers
Reverse grading – smallest grains are on the bottom and largest grains are on the top.

37.  What are ripple marks?
Ripple marks are caused by the action of wind or water on sand.

38.  What are mud cracks?
They form when muddy deposits dry and shrink.

39.  Fossils and Concretions
Fossils are remains of traces of ancient plants and animals. They are preserved in the sedimentary rock.
Concretions are formed when minerals precipitate from fluids and build up around a nucleus.
Geodes are minerals that crystallize inside the cavities to form a rock.

40. Section 4: Metamorphic Rocks

41.  What is metamorphism?
Metamorphism is the process by which heat, pressure and chemical processes change one type of rock to another.

42.  Formation of Metamorphic Rocks
The type of rock that forms can indicate the conditions that occurred when the original rock changed.
Two types occur in the Earth’s crust.
Small volumes of rock come into contact with magma
Large area of Earth’s crust are affected by heat and pressure caused by movement of tectonic plates.

43.  What is contact metamorphism?
Heat from magma can change the structure and mineral composition of the surrounding rocks.
Hot chemicals moving through fractures of the rock could also change the rock.

44.  What is regional metamorphism?
Metamorphism usually occurs in an area of thousands of square kilometers during periods of high tectonic activity.

45.  Classification of Metamorphic Rocks
Minerals in the original rock determine the mineral composition of the metamorphosed rock
Metamorphic rocks are first classified by their texture – foliated or nonfoliated.

46.  What is foliation?
Foliation is the metamorphic rock texture in which mineral grains are arranged in planes or bands.
Extreme pressure could cause mineral crystals to reform or regrow.
Minerals of different compositions separate to produce light and dark bands.

47.  Example of Foliated Rocks
Slate occurs when shale (a sedimentary rock) goes through extreme pressure.
Sheets of slate are used for shingles or walkway stones
Slate can form schist which can form gneiss because of heat and pressure.

49.  What are nonfoliated rocks?
Rocks that do not have bands or aligned minerals.
Original rock may have contained just one mineral or a small amount of another
Original rock contained grains that are round or square
Quartzite is formed from quartz sandstone
Marble is formed from limestone.