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Chapter 6
Rocks
Section 1 Rocks and the Rock Cycle
Three Major Types of Rocks
1. Igneous _________________________________________
____________________________________________
2. Sedimentary - ________________________________________
Types of sediments
1. rock fragments
2. plant and animal remains
3. chemicals (water)
3. Metamorphic - _______________________________________
Rock Cycle - any rock can become either:
Igneous
Sedimentary
Metamorphic
depending on how it is influenced by the environment.
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Properties of Rocks
Bowens Reaction
Canadian geologist in 1928 proposed a hypothesis on the
formation of minerals.
As the magma cools different minerals can form.
Chemical Stability of Minerals
Physical Stability of Rocks
Section 2 Igneous Rocks
Formation of Magma
Magma
__________________________________________________
Lava
_________________________________________________
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Textures of Igneous Rocks
1. _____________ - formed outside the earth's crust from lava.
____________ exited from the earth
2. ______________ - formed within the crust from the magma.
____________ inside the earth
TEXTURE depends on the size of the rock crystals. The rate of
cooling determines crystal size.
a. Intrusive
_________ cooling - ___________ mineral grains
(plutonic after the Roman God of the underground Pluto)
ex. __________ - course grained
b. Extrusive
cools _________ - ___________ mineral grains
(volcanic)
ex. __________- fine grained
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c. intermediate cools
________________________________
ex. Obsidian
Vesicular
____________________________________________________
PORPHYRY - (Por Fi Ree) - rocks with two textures
a.
One mineral solidifies - forms large crystals
b.
The other mineral solidifies later - there is less room - therefore
the crystals are smaller.
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Intrusive Igneous Rocks
Batholiths and Stocks
_________________________
Large igneous intrusions at least 100kms.
Forms mountain bases like Sierra Nevada in Cal.
_________________________
Smaller than 100kms
_________________________
When magma pushed up between rock layers, if forms a dome
Black Hill of South Dakota
Sills and Dikes
______________ are parallel layers, small area between layers
______________ cut across rock layers
Intrusive Igneous Rocks
When lava hardens on the surface.
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Composition of Igneous Rocks
___________________
High silica acid type of magma.
NOT much Ca, Fe or Mg only light colored Si.
Mostly intrusive magma - slow thick - does not reach the surface easily.
Forms granite, quartz, orthoclase feldspar.
___________________
Low Si concentrations
High in Ca, Fe and Mg
Much hotter - easier to flow to the surface, extrusive
Forms basalt and gabbro
___________________
Made up of mostly plagioclase feldspar, hornblende, pyroxene,
and biotite mica.
Diorite and andesite
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Section 3 Sedimentary Rocks
Formed from sediments bound together in some way
Formation of Sedimentary Rocks
Compaction
______________________________________________________.
Cementation
____________________________________________________.
These cements enter the pore spaces between sediments. They glue
them together to make a clastic sediment rock
Types of cement:
1. Silica - from weathered quartz - grey or white
2. Lime - from weathered calcite - grey or white
3. Iron - from weathered Fe containing rock - red or brown
4. Pressure can act as a cement in clay and silt.
Chemical Sedimentary Rock
Forming Chemically Derived Sedimentary Rocks
__________________________________________________
________________________________________________
Limestone tiny grains of calcite deposited in the seas or lakes.
Grey or tan in color. Smooth and dense.
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Rock Salt - table salt - made of mineral Halite. Forms when salt
water dries up, the salt is left behind. Found in thick layers
around the world.
Gypsum
Found in layers around the world. Formed from mineral gypsum.
Organic
Formed from remains of once living organisms (plants and animals)
Coal- plant remains
Fossil limestone
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Chert
Clastic Sedimentary rocks
1. Fragments must come from pre-existing rocks
2. Fragments come from weathering and erosion
agents:
________________________
________________________
________________________
3. Fragment sizes - ______________________________________
_________________________________________________
4. Fragments need to be cemented together to make rocks.
Conglomerate - very course mixture of rounded pebbles and sand of
various different sediment types (breccia is angular fragments).
Sand Stone - grains of quartz cemented together. Very porous with a
lot of small holes or openings. Permeable, able to absorb
water.
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Shale - tiny flakes of kaolin (clay). Held together by pressure, not
cement. Very tiny holes, cannot absorb water. Smooth and
easily broken.
Characteristics of Clastic Sediments
The characteristics of the sediments are determined by the way they
are transported and deposited.
4 ways sediments are transported
1. Water
2. Ice
3. Wind
4. Gravity
Sorting
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River Deposits A river's motion causes it to carry sediment. When the river slows it
cannot carry its sediments. Sediments fall to the bottom.
Angularity
Not rounded sediments. Broken and sharper edges.
Sedimentary Rock Features
1. __________ - visible layers (beds) within rocks or rock structures.
This layering is caused by changes in the rock materials.
ex. a layer of Sand
a layer of Clay
a layer of Silt
2. _________________________________
Cross bedding - bedding layers formed near or on sand dunes
or river delta's - not flat but slanted
Graded Beds - different types of materials deposited within a
layer
3. _____________________________
Caused when wind or water left a mark on the sandy surface
and hardened.
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4.
_______________________________________
Occur when clay and silt dry, they contract and spaces form.
These spaces can get buried and become rock.
5. Fossils and Concretions
_______________________
Are remains, impressions or other evidence of existing plants and
animals preserved in rocks.
*Only Found in Sedimentary Rocks!!!!
Animal dies - bone does not decay, it gets buried. Rock eventually
decays but a hole is left. The hole fills in with minerals, the minerals
harden, a fossil is formed.
_________________ - nodules or "lumps" of fine grained silica.
Chert - name of silica
Flint - dark grey or black chert
______________Limestone with hollow spheres that are lined
with quartz or calcite crystals.
Limestone middle dissolves in water, then the water
deposits quartz or calcite.
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Section 4 METAMORPHIC ROCKS Are made from existing rocks by the action of:
1. __________________________
2. __________________________
3. __________________________
Formation of Metamorphic Rock
_____________________________
1. hot magma moves into rocks, heating and changing in
2. occurs in a small area
3. chemical change occurs by rearranging the minerals forming
a new rock.
4. the rock does not melt, it is rearranged.
_______________________________________
major source of metamorphic rock. Occurs in large areas,
often associated with mountain building.
Classification of Metamorphic Rock
Properties of metamorphic rock depend on the parent rock or the
minerals in the original rock. The parent rock’s characteristics
and traits can be seen in certain metamorphic rocks.
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Foliated Rocks
1. ___________________________________________
2. ___________________________________________
3. Include
Slate
Schist
Gneiss
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Nonfoliated Rocks
____________________________________________________
Distortion or deformation:
1.
___________________________________________
2.
sedimentary rock gets laid down in horizontal layers
3.
they get buried deep within the earth and are subjected to
low heat and pressure; like where there is a fault line.
4.
grains of rock get squeezed together and the heat rearranges minerals - a new different rock is formed.
Quartzite
Marble
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