Classifying Rocks

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Table of Contents

• Classifying Rocks
• Igneous Rocks
• Sedimentary Rocks
• Rocks from Reefs
• Metamorphic Rocks
• The Rock Cycle

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Studying Rocks
- Classifying Rocks

• When studying a rock sample, geologists observe
  the rocks mineral composition, color, and
  texture.

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Mineral Composition and Color
- Classifying Rocks

• Rock a solid mixture of minerals and other
  materials.
• Rock-forming minerals the common minerals that
  make up most of the rocks of Earths crust.
• Granite tends to be a light-colored rock that
  has high silica content
• Basalt tends to be a dark-colored rock that is
  low in silica

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Texture
- Classifying Rocks

• Grains particles of minerals or other rocks
  that give a rock its texture.
• Texture the look and feel of a rocks surface,
  determined by the size, shape, and pattern of a
  rocks grains.

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Texture
- Classifying Rocks

• Grain size
• Coarse-grained large easy to see grains
• Fine-grained so small they can only be seen
  under a microscope

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Texture
- Classifying Rocks

• Grain Shape varies greatly from sand grains to
  large triangular grains
• Grain Pattern can vary also from layers to
  swirls to bands

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How Rocks Form
- Classifying Rocks

• Geologists classify rocks into three major
  groups
• igneous rock, sedimentary rock, and metamorphic
  rock.

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How Rocks Form
- Classifying Rocks

• Igneous rock type of rock that forms from the
  melting then cooling of molten rock at or below
  the surface.
• Sedimentary rock type of rock that forms when
  particles from other rocks or the remains of
  plants and animals are pressed and cemented
  together.
• Metamorphic rock type of rock that forms from
  an existing rock that is changed by heat and
  pressure

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Classifying Igneous Rocks
- Igneous Rocks

• Igneous rocks are classified according to their
  origin, texture, and mineral composition.

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Classifying Igneous Rocks

• Extrusive igneous rock forms from lava on
  Earths surface.
• Intrusive igneous rock forms when magma hardens
  beneath Earths surface.
• The faster igneous rock cools, the finer the
  grains
• Extrusive igneous rock tends to be a
  finer-grained rock than intrusive igneous rock

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Mineral Mixture
- Igneous Rocks

• Granite is a mixture of light-colored minerals,
  such as feldspar and quartz, and dark-colored
  minerals, including hornblende and different
  types of mica. But granite can vary in mineral
  composition. This affects its color and texture.

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Mineral Mixture
- Igneous Rocks

• Reading Graphs
• What mineral is most abundant in granite?

• Feldspar

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Mineral Mixture
- Igneous Rocks

• Reading Graphs
• About what percentage of granite is made up of
  dark minerals?

• 10

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Mineral Mixture
- Igneous Rocks

• Calculating
• If the amount of quartz increases to 35 percent
  and the amount of dark-colored minerals stays the
  same, what percentage of the granite will be made
  up of feldspar?

• 100 - (35 10) 55

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Mineral Mixture
- Igneous Rocks

• Predicting
• How would the color of the granite change if it
  contained less feldspar and more mica and
  hornblende?

• The overall color would be darker.

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Links on Igneous Rocks
- Igneous Rocks

• Click the SciLinks button for links on igneous
  rocks.

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From Sediment to Rock
- Sedimentary Rocks

• Most sedimentary rocks are formed through a
  series of processes erosion, deposition,
  compaction, and cementation.

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From Sediment to Rock
- Sedimentary Rocks

• Sediment small, solid pieces of material that
  come from rocks or organisms.
• Usually forms due to erosion
• Erosion a destructive process in which water or
  wind loosens and carries away fragments of rock.
• Deposition process by which sediment settles
  out of the water or wind that is carrying it.

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From Sediment to Rock
- Sedimentary Rocks

• Compaction process by which sediments are
  pressed together under their own weight.
• Occurs over millions of years as layers build
• Cementation process by which dissolved minerals
  crystallize and glue particles of sediment
  together into one mass.
• Takes place when sediment is in the presence of
  water

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Types of Sedimentary Rock
- Sedimentary Rocks

• There are three major groups of sedimentary
  rocks
• clastic rocks, organic rocks, and chemical rocks.
• Clastic rock sedimentary rock that forms when
  rock fragments are squeezed together under high
  pressure.
• Can range in size from microscopic clay particles
  to large boulders
• Ex shale, sandstone, conglomerate, and breccia

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Types of Sedimentary Rock
- Sedimentary Rocks

• Organic rock sedimentary rock that forms from
  remains of organisms deposited in thick layers.
• Ex Coal and Limestone
• Coal forms from the remains of swamp plants
  buried in water.
• Limestone forms in the ocean, where many living
  things, such as coral, clams, and oysters, have
  hard shells made of calcite that collect on the
  ocean floor.

Peat
Lignite
Bituminous
Anthracite
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Types of Sedimentary Rock
- Sedimentary Rocks

• Chemical rock sedimentary rock that forms when
  minerals crystallize from a solution. (Reacts to
  HCl)
• Ex Limestone forms from calcite deposits
  dissolved in lakes, rivers, streams.

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Uses of Sedimentary Rock
- Sedimentary Rocks

• Sedimentary rock has been used for thousands of
  years in building structures, tools, and
  statues.
• Ex The White House in Washington D.C. is
  constructed of sandstone.

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Links on Sedimentary Rocks
- Sedimentary Rocks

• Click the SciLinks button for links on
  sedimentary rocks.

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Coral Reefs
- Rocks From Reefs

• Coral reef a structure of calcite skeletons
  built up by coral animals in warm, shallow ocean
  water.
• When coral animals die, their skeletons remain.
  More corals build on top of them, gradually
  forming a coral reef.
• Only form in ocean water between 30N and 30S
  latitude

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Coral Reefs(not in notes)

• Coral reef is really organic(from living things)
  limestone.
• Deposits of organic limestone help geologists
  figure out what the environment was like long
  ago.
• If they find a fossil of coral reef, they would
  know that location used to contain warm, shallow
  ocean water.

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More on Coral Landforms
- Rocks From Reefs

• Click the PHSchool.com button for an
  activityabout coral landforms.

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Metamorphic Rock
- Metamorphic Rocks

• Metamorphic rock forms when heat and pressure
  beneath Earths surface changes the appearance,
  texture, crystal structure, and mineral content
  of either igneous, sedimentary, or other
  metamorphic rock.

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Types of Metamorphic Rocks
- Metamorphic Rocks

• Geologists classify metamorphic rocks according
  to the arrangement of the grains that make up the
  rocks.
• Foliated rocks metamorphic rocks that have
  grains arranged in parallel layers or bands.
• Ex Slate metamorphic shale (denser and more
  compact than shale)

Shale
Slate
Gneiss
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Types of Metamorphic Rocks
- Metamorphic Rocks

• Nonfoliated rocks metamorphic rocks that have
  randomly arranged metamorphic grains that do not
  split into layers
• Ex Quartzite metamorphic sandstone
• Marble metamorphic limestone

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Links on Metamorphic Rocks
- Metamorphic Rocks

• Click the SciLinks button for links on
  metamorphic rocks.

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A Cycle of Many Pathways
- The Rock Cycle

• Forces deep inside Earth and at the surface
  produce a slow cycle that builds, destroys, and
  changes the rocks in the crust.

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- The Rock Cycle

• Rock cycle processes on the surface and inside
  Earth that slowly change rocks from one kind to
  another.

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The Rock Cycle and Plate Tectonics
- The Rock Cycle

• Plate movements start the rock cycle by helping
  to form magma, the source of igneous rocks.
• Plate movements also cause faulting, folding, and
  other motions of the crust that help to form
  sedimentary and metamorphic rocks.

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Rock Cycle Activity
- The Rock Cycle

• Click the Active Art button to open a browser
  window and access Active Art about the rock cycle.

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- The Rock Cycle
Igneous
Metamorphic
Sedimentary
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Graphic Organizer
Metamorphic
Igneous
Organic
Foliated
Extrusive
Chemical