Download Rocks Section 1: Classifying Rocks »Grain Size

Ch. 2
Rocks
Section 1:
Classifying Rocks
Classifying Rocks
» When studying rock samples,
geologists look at 4 aspects:
–Origin
–Color
–Texture
–Mineral composition
Classifying Rocks
» We are going to take a closer look at
Texture!
– Again, texture is the look and feel of a
rocks surface.
Texture is broken down into
4 main groups:
1 grain size
3 grain pattern
2 grain shape
4 no visible grain
Classifying Rocks
–What is a rock made of?
» Rock–A lump or mass of consolidated
mineral material, rock fragments,
and organic matter.
» Color-
Classifying Rocks
– What colors do you see.
» Texture-
– The look and feel of the rocks surface.
» Origin-
– Where the rock was created.
» Mineral composition-
– Using a microscope to observer the
crystal shape and size of a rock.
Classifying Rocks Texture
»Grain Size
–Fine-grained:
•rocks that cools fast.
•small and hard to see grains.
–Coarse-grained:
•rocks that cools slow.
•Large and easy to see grains.
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Classifying Rocks Texture
» Fine grained
»Grain Shape
–What shapes you see in the grains.
–Some look like:
•Sand, stars, seeds, crystals, etc.
» Coarse-grained
–Others can be rounded or jagged.
Classifying Rocks Texture
» Conglomerate
»Breccia
»Grain Pattern
–Layers
–Wavy or swirls
–Random
Classifying Rocks Texture
»No Visible Grain
–Fast cooling rocks that form no
crystal grain. (obsidian)
Or other form from–Very fine particles of silica that
have settled out of water. (flint)
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Classifying Rocks
Classifying Rocks Texture
» There are 3 main groups of
rocks:
–Igneous Rocks
–Sedimentary Rocks
–Metamorphic Rocks
» Igneous Rocks– Forms from cooling of molten material.
» Sedimentary Rocks– Forms from fragments and particles of
rocks that are compacted and cemented
together.
» Metamorphic Rocks– Form from existing rocks that have been
changed by heat, pressure, or chemical
reactions deep underground.
Review
»What are rocks made out of?
»What is texture?
»What are the different
aspects of texture?
»What the 3 types of rocks?
Ch. 2
Rocks
Section 2:
Igneous Rocks
3
Igneous Rocks
Igneous Rocks
*95% of Earth’s crust is composed of
igneous rocks or metamorphic rocks
formed from igneous rocks.
Igneous Rocks are classified by:
– Origin
– Color
– Texture
– Mineral composition
Origin» Extrusive rock– Forms at the surface when lava cools
and hardens. (basalt)
» Intrusive rock– Forms when magma cools and hardens
below the surface. (granite)
Igneous Rocks
Composition
– Fine-grain and
fast cooling
Light
Mostly quartz and
light feldspar
with few dark
minerals
– Coarse-grain
and slower
cooling
Coarse Grained
Granite*
Fine Grained
(quartz crystals
common)
Rhyolite
Texture
Fragmental
(Broken)
» Vesicular =
– rock with holes - vesicular "basalt"
» Porphyritic =
– the rock is mostly fine but has some
large crystals - porphyritic "basalt"
Diorite
(no quartz)
Dark
Mostly dark
feldspar and
other dark
minerals
Gabbro
Andesite
(no quartz
crystals;
greyish)
Glassy
Vesicular
Special Features of Igneous rocks
Mixed
A mixture of light
feldspars and
dark minerals
Basalt*
Obsidian
Pumice
Scoria
Tuff - cemented together fragments of volcanic ash,
and debris
Igneous Rocks
» Mineral composition–Light colored = high silica content
–Dark colored = low silica content
» All igneous rocks are
composed of many different
minerals in different amounts.
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Ch. 5
Rocks
Section 3:
Metamorphic Rocks
» Metamorphic Rocks–Form from existing rocks that have
been changed by heat, pressure, or
chemical reactions deep
underground.
–Changes the appearance, texture,
and crystal structure of the rock.
•Meta means “change” and
morphosis means “form”.
Formation of Metamorphic Rocks
» Metamorphism
– Temperature exceeds 250 0C or 480 0F
– Some temperatures reach 800 0C or 1,475 0F
– Pressure exceeds 2,000 kb – 10,000 kb or
(approx. 10 km deep and deeper)
» Metamorphism ends when melting
begins
– Melting begins at ~700 OC for most rocks
some melt at much lower temperatures.
Formation of Metamorphic Rocks
2 major ways in which Metamorphic
rocks form:
» 1) Convergent Plate Boundaries– When two tectonic plates collide, extreme
pressures and temperatures are applied to
rocks.
» 2) Magma rising– Magma plums rise to the surface providing
the heat needed to change rocks.
Formation of Metamorphic Rocks
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» Metamorphism can be any
rock type: igneous, sedimentary,
or metamorphic.
Shale
Quartzite
Schist
Sandstone
» Gneiss– Granite that has been changed under
heat and pressure.
Classifying Metamorphic Rocks-
» Foliated– Rock grains are arranged in a particular
pattern.
» Nonfoliated– Rock grains are arranged randomly.
Foliated
Nonfoliated textures
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Ch. 2
Rocks
Section 4:
Sedimentary Rocks
Sedimentary Rocks
» Sedimentary Rocks– Forms from fragments and particles of
rocks that are compacted and cemented
together.
– The particles (sediments) deposited by
water and wind.
» Sediments-
– Are small pieces of material that comes
from rocks or living things.
Sedimentary Rocks Formation
The 4 steps of sedimentary rock
Formation:
» 1) Weathering & Erosion– The breaking down and movement of
rocks by wind, water, ice, or chemically.
» 2) Deposition– When sediments settles out of the water
or wind carrying it.
Sedimentary Rocks Formation
» 3) Compaction– The process of pressing sediments
together.
» 4) Cementation– When dissolved minerals crystallize
and glue sediments together.
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Types of Sedimentary Rocks
» 1) Detrital or Clastic Rock–Forms when rock fragments are
squeezed together.
Gravel: Grain size greater than 2 mm
Rock Type:
-rounded clast = conglomerate
-angular clasts = breccia
•Detrital means “ to wear away”
•Clastic means “rock”
–Examples: shale, sandstones,
conglomerates, etc.
Sand: Grain size 1/16 to 2 mm
Rock Type: Sandstone
Shale
-dominated by quartz grains = quartz sandstone
-dominated by feldspar grains = arkose
-dominated by rock fragments = graywacke)
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Types of Sedimentary Rocks
» 2) Organic Rocks-
[fossileferous]
limestone
–Form from the remains of plants
and animals in thick layers.
•Organic means “living”
–Examples: coal and limestone.
[micritic] limestone
Coquina
-fossil hash cemented together
-may resemble granola
Chalk
-microscopic planktonic organisms
(coccolithophores) (fizzes in acid)
Types of Sedimentary Rocks
» 3) Chemical Rocks–Form when minerals that are
dissolved in a solution crystallize.
• Chert - microcrystalline quartz
– Various modes of formation
•Evaporites
– Rock salt - halite
– Gypsum
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Review
–What are sedimentary rocks made
of?
–How do they form?
–What are the 3 types of sedimentary
rocks?
Review
–How do rocks become
metamorphic?
–What are the 2 main ways in
which rocks are
metamorphosed?
– How are they classified?
Ch. 5
Rocks
Review
Classifying Rocks
–What is a rock made of?
» Rock–A lump or mass of consolidated
mineral material.
–A mixture of several different
mineral particles called Grains.
» Color-
Classifying Rocks
– What colors do you see.
» Texture– The look and feel of the rocks surface.
» Mineral composition– Using a microscope to observer the
crystal shape and size of a rock.
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Classifying Rocks
» We are going to take a closer look at
Texture!
– Again, texture is the look and feel of a
rocks surface.
Texture is broken down into
4 main groups:
1 grain size
3 grain pattern
2 grain shape
4 no visible grain
Classifying Rocks Texture
»Grain Shape
–What shapes you see in the grains.
–Some look like:
•Sand, stars, seeds, crystals, etc.
–Others can be rounded or jagged.
Classifying Rocks Texture
»No Visible Grain
–Fast cooling rocks that form no
crystal grain. (obsidian)
Or other form from–Very fine particles of silica that
have settled out of water. (flint)
Classifying Rocks Texture
»Grain Size
–Fine-grained:
•rocks that cools fast.
•small and hard to see grains.
–Coarse-grained:
•rocks that cools slow.
•Large and easy to see grains.
Classifying Rocks Texture
»Grain Pattern
–Layers
–Wavy or swirls
–Random
» Igneous Rocks– Forms from cooling of molten material.
» Sedimentary Rocks– Forms from fragments and particles of
rocks that are compacted and cemented
together.
» Metamorphic Rocks– Form from existing rocks that have been
changed by heat, pressure, or chemical
reactions deep underground.
11
Igneous Rocks
*95% of Earth’s crust is composed of
igneous rocks or metamorphic rocks
formed from igneous rocks.
Igneous Rocks are classified by:
– Origin
– Color
– Texture
– Mineral composition
Special Features of Igneous rocks
» Vesicular =
– rock with holes - vesicular "basalt"
» Porphyritic =
– the rock is mostly fine but has some large
crystals - porphyritic "basalt"
Sedimentary Rocks
» Sedimentary Rocks– Forms from fragments and particles of
rocks that are compacted and cemented
together.
– The particles (sediments) deposited by
water and wind.
» Sediments-
– Are small pieces of material that comes
from rocks or living things.
Igneous Rocks
Origin» Extrusive rock– Forms at the surface when lava cools
and hardens. (basalt)
» Intrusive rock– Forms when magma cools and hardens
below the surface. (granite)
Igneous Rocks
» Mineral composition–Light colored = high silica content
–Dark colored = low silica content
» All igneous rocks are
composed of many different
minerals in different amounts.
Sedimentary Rocks Formation
The 4 steps of sedimentary rock
Formation:
» 1) Erosion– The breaking down of rocks by wind or
water.
» 2) Deposition– When sediments settles out of the
water or wind carrying it.
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Sedimentary Rocks Formation
» 3) Compaction– The process of pressing sediments
together.
» 4) Cementation– When dissolved minerals crystallize
and glue sediments together.
Types of Sedimentary Rocks
» 1) Clastic Rock–Forms when rock fragments are
squeezed together.
•Clastic means “rock”
•Remember Pyroclastic = “fire-rock”
–Examples: shale, sandstones,
conglomerates, etc.
Types of Sedimentary Rocks
» 3) Chemical Rocks–Form when minerals that are
dissolved in a solution crystallize.
• Chert - microcrystalline quartz
– Various modes of formation
•Evaporites
– Rock salt - halite
– Gypsum
Types of Sedimentary Rocks
» 2) Organic Rocks–Form from the remains of plants
and animals in thick layers.
•Organic means “living”
–Examples: coal and limestone.
» Metamorphic Rocks–Form from existing rocks that have
been changed by heat, pressure, or
chemical reactions deep
underground.
–Changes the appearance, texture,
and crystal structure of the rock.
•Meta means “change” and
morphosis means “form”.
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Formation of Metamorphic Rocks
Formation of Metamorphic Rocks
2 major ways in which Metamorphic
rocks form:
» 1) Convergent Plate Boundaries– When two tectonic plates collide, extreme
pressures and temperatures are applied to
rocks.
» 2) Magma rising– Magma plums rise to the surface providing
the heat needed to change rocks.
Classifying Metamorphic Rocks-
» Foliated– Rock grains are arranged in a particular
pattern.
» Nonfoliated– Rock grains are arranged randomly.
Rock Cycle
Classifying Rocks
–Granite is composted of 3
different minerals:
–Feldspar (50% or greater)
–Quartz (25-40%)
–Mica (3-10%)
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» Crystals of the minerals that
make of the rock garnet.
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