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Chapter Two: Rocks:  Materials of the Lithosphere

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Chapter Two Learning Objectives:

  1. Diagram and discuss the rock cycle.
  2. List the geologic processes involved in the formation of each rock group.
  3. Briefly explain crystallization of magma.
  4. List the criteria used to classify igneous rocks.
  5. List the names, textures, and environments of formation for the most common igneous rocks.
  6. Discuss the origin of materials that accumulate as sediment.
  7. List the criteria used to classify sedimentary rocks.
  8. Explain the difference between detrital and chemical sedimentary rocks.
  9. List the names, textures, and environments of formation for the most common sedimentary rocks.
  10. List the common features of sedimentary rocks.
  11. Describe the agents of metamorphic rocks.
  12. List the criteria used to classify metamorphic rocks.
  13. List the names, textures, and environment of formation for the most common metamorphic rocks.
  14. Discuss metallic and nonmetallic mineral resources.

Chapter Two Outline:

Rock Cycle

Shows the relations among the three rock types

Proposed by James Hutton in the late 1700's

The cycle

Magma

Crystallization

Igneous rock

Weathering

Transportation

Deposition

Sediment

Lithification

Sedimentary Rock

Metamorphism

Metamorphic rock

Melting

Magma

 

Rock Cycle continued

Full cycle does not always take place due to " shortcuts " or interruptions

Sedimentary rock melts

Igneous rock is metamorphosed

Sedimentary rock weathers

Metamorphic rock weathers

 


Igneous Rock

Forms as magma cools and crystallizes

Rocks formed inside Earth are called plutonic or intrusive rocks

Rocks formed on the surface

Formed from lava (a material similar to magma, but without gas)

Called volcanic or extrusive rocks

 

Igneous rock continued

Crystallization of magma

Ions are arranged into orderly patterns

Crystal size of the rock is determined by the rate of cooling

Slow rate forms large crystals

Fast rate forms microscopic crystals

Very fast rate forms glass

 

Igneous rock continued

Classification is based on the rock's texture and mineral composition

Texture

Size and arrangement of crystals

Types

Fine-grained ----- fast rate of cooling

Coarse - grained ------ slow rate of cooling

Porphyritic ( two crystal sizes ) -- two rates of cooling

Glassy ----- very fast rate of cooling

 

Igneous rock continued

Mineral composition

Explained by Bowen's reaction series which shows the order of mineral crystallization

Influenced by crystal settling in the magma

 

Naming Igneous Rocks

Basaltic rocks

Derived from the first minerals to crystallize

Rich in iron and magnesium

Low in silica

Common rock is basalt

Granite rocks

From the last minerals to crystallize

Mainly feldspar and quartz

High silica content

Common rock is granite

 


Sedimentary rocks

Form from sediments (weathered products )

Form about 75 % of the rock outcrops on the continents

Used to construct much of Earth's history

Clues to past fossils

Provide information about sediment transport

Rocks often contain fossils

 


Economic importance

Coal

Petroleum and natural gas

Source of iron and aluminum

 

Classification

Two groups based on the source of the materials

Detrital rocks

Material is solid particles

Classified by particle size

Common rocks are:

Shale ( most abundant)

Sandstone

Conglomerate

Siltstone

 

Classification continued

Chemical rocks

Derived from material that was once in solution and precipitates to form sediment

Directly precipitated or

Through life processes (bio-chemical origin)

 

 

Common Rocks

Limestone - the most abundant chemical rock

Travertine

Microcrystalline quartz

Chert

Flint

Jasper

Agate

Evaporates

Rock salt

Gypsum

Coal

Lignite

Bituminous

 


Produced through lithification

Loose sediments are transformed into solid rock

Lithification processes

Compaction

Cementation by the materials

Calcite

Silica

Iron oxide

 

FEATURES

Strata, or beds

(most characteristic)

Bedding planes separate strata

Fossils

Traces or remains of prehistoric life

Are the most important inclusions

Help determine past environments

Used as time indicators

Used for matching rocks from different places

 

 


Metamorphic rocks

"Changed form" rocks

Can form from

Igneous rocks

Sedimentary rocks

Other metamorphic rocks

 

Degrees of metamorphism

Show in the rock's texture and mineralogy

Types

Low - grade ( e.g., shale becomes slate )

High - grade ( causes the original features to be obliterated )

 


Metamorphic settings

Regional metamorphism

Over extensive areas

Produces the greatest volume of metamorphic rock

Contact metamorphism

Near a mass of magma

" Bakes " the surrounding rock

 


Metamorphic agents

Heat

Pressure

From burial

From stress

Chemically active fluids

Water (most common fluid)

Ion exchange among minerals

Textures

Foliated

Minerals are in a parallel alignment

Minerals are perpendicular to the force

Nonaffiliated

Contain equidimensional crystals

Resembles a coarse igneous rock

 

CLASSIFICATION

Based on texture

Two groups

Foliated rocks

Nonfoliated

 

Foliated
Rocks

Slate

Fine - grained

Splits easily

Schist

Strongly foliated

" Platy "

Types based on composition

(e.g., mica schist)

Gneiss

Strong segregation of silicate minerals

" Banded " texture

 

Nonfoliated rocks

Marble

Parent rock - limestone

Calcite crystals

Used as a building stone

Variety of colors

Quartzite

Parent rock - quartz sandstone

Quartz grains are fused

 

Resources from rocks and minerals

Metallic mineral resources

e.g., Gold, silver, copper

Produced by

Igneous processes

Metamorphic processes

 

Resources from rocks and minerals

Hydrothermal (hot-water) solutions

Hot

Contain metal - rich fluids

Associated with cooling magma bodies

Types

Vein deposits occur in fractures or bedding planes

Disseminated deposits are distributed throughout the rock

 


Nonmetallic mineral resources

Make use of the materials

Nonmetallic elements

Physical or chemical properties

Two broad groups

Building materials (e.g., limestone, gypsum)

Industrial minerals ( e.g., fluorite, corundum, sylvite)

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