Rocks: Materials of the Solid Earth

Chapter 2

Earth Science, 6e

Modified by Dr. Kane

What is a Rock?

How would you define a rock and a mineral?

What types of Rocks are there?

Igneous Rocks: from magma or lavaOrigin: igneous activity

• Example: granite or basalt

Sedimentary rocks: from sedimentsOrigin: weathering and erosionExample: sandstone or clay

Metamorphic rocks: from stressOrigin: mountain buildingExample: gneiss or marble

The rock cycle (page 45)

PART – I: IGNEOUS ROCKS

FEEDBACK:

From what process igneous rocks from?

Plate Margins

• Divergent: Plates pull apart

Example: Mid ocean ridge; Rift

• Convergent: Plate come together– Ocean – Continent; Ex: Cascades, Andes– Ocean – Ocean; Ex: Japan, Caribbean– Continent – Continent; Himalaya

• Transform Fault: Plates slide

Origin of Magma (page 228)

Magma forms at three major geological settings:

• Divergent (Ex: Mid ocean ridge)

• Convergent (Ex: Cascades volcanoes)

• Intra plate Not a plate margin (Ex: Hawaii, Hot spot)

Origin of Magma (page 148)

Mid Ocean Ridge (divergent)

Subduction Zone (Convergent)

Causes of Magma Formation

Decompression Melting (opening a bottle of soda)

Factors influencing magma formation:

1. Heat Increase2. Reduction of confining Pressure

Role of volatiles (gases)

Types of Igneous rocks

Magma cools and crystallizes Inside the crust → Plutonic or Intrusive rocks

Lava cools and crystallizes Outside the crust → volcanic or extrusive rocks

Classification of Igneous rocks

When identifying Igneous rocks look for:

1. Grain Size (TEXTURE)

and

2. Rock color (CHEMICAL COMPOSITION)

Rate of Cooling and Crystal Size

• Texture is size and arrangement of crystals

• Crystal size is determined by the rate and depth of cooling of magma/lava

• Slow rate forms large crystals • Fast rate forms microscopic crystals • Very fast rate forms glass

Feedback:

The slower the rate of cooling, the smaller / larger the crystals?

Types of Textures

Phaneritic: Coarse grain/slow cooling rate

Example: Granite or DioriteAphanitic: Fine grain/fast cooling rate

Example: basalt or rhyoliteGlassy: glasslike/very fast cooling rate

Example: Obsidian (volcanic rock)

Types of Textures

Porphyritic: Slow then rapid coolingExample: porphyry basalt, porphyry granite

Vesicular: Full of holes due to gases Example: Vesicular basalt, scoria, and pumice

Pyroclastic: Angular volcanic fragments cemented by ash from violent eruptions Example: tuff

Photomicrograph

Photomicrograph

What’s the texture?

What’s the texture?

What’s the texture?

What’s the texture?

What’s the texture?

Obsidian Aztec

Temple Mayor, Mexico

Chemical Classification of Igneous rocks

• Bowen's reaction series (page 53):• Minerals form in a systematic order

through

Discontinuous series (Olivine to Quartz) and

Continuous series (Feldspars series)

• Magmatic Differentiation

First to form settle at the bottom

Feedback

• Which mineral crystallizes first?

• Which mineral crystallizes last?

Question

• Can Olivine and Quartz be found together in the same rock?

• Why? …

Naming Igneous rocks

Granitic or Felsic rocks

• Light-colored rocks

• Rich in silica/poor in Fe and Mg

• Form from melting of continental crust

• Common rock is Granite (intrusive) or Rhyolite (volcanic)

Naming Igneous rocks

Basaltic or Mafic/ultramafic Rocks

• Dark Rocks• Rich in Fe and Mg/poor in silica • Originate mostly from the oceanic crust at mid-

ocean ridge, and the upper mantle• Common rock is Basalt (volcanic) or Gabbro

(plutonic)

Texture? Mafic or Felsic?

Texture? Mafic or Felsic?

Naming Igneous rocks

Intermediate or Andesitic Rocks

• Mineral and chemical composition are average of felsic and mafic rocks

• Has dark minerals (pyroxene, amphibole, and mica) and light minerals (feldspar and quartz)

• Silica content: 50%<SiO2 <60%

• Common rock is Andesite (volcanic) or Diorite (intrusive)

• Found mostly at Suduction Zone

Naming Igneous Rocks

Ultramafic Rocks

• Dark rocks

• Very poor in silica: SiO2 <45%

• Originates from lower mantle and is found in oceanic floor at mid-ocean ridge along mafic rocks

• Typical rock is peridotite (intrusive) or Komatiite (volcanic)

Classification of igneous rocks

PART – II: Sedimentary rocks

FEEDBACK

From what geological process sedimentary rocks form?

Weathering

Two kinds of weathering 1. Mechanical weathering

• Breaking of rocks into smaller pieces

• Processes of mechanical weathering• Frost wedging (freezing and thawing/exfoliation)

• Unloading (exposure to surface)

• Biological activity (burrow animals)

Frost wedging (page 55)

Joint-controlled weathering in igneous rocks

Unloading and exfoliation of igneous rocks

Weathering

Two kinds of weathering 2. Chemical weathering

• Alters the internal structures of minerals by removing or adding elements

• Most important agent is water

• Oxygen dissolved in water oxidizes materials

• Carbon dioxide (CO2) dissolved in water forms

carbonic acid and alters the material

Factors of weathering

Important factors • Climate (heat and moisture)

• Chemical weathering is most effective in areas of warm temperatures and abundant moisture

Chemical Weathering

Weathering of granite minerals

• Weathering of potassium feldspar produces clay

Sedimentary Rocks

Lithification: 1.Compaction of loose sediment through

confining pressure of overlying rocks

2.Cementation of loose sediment by

• Calcite

• Silica

• Iron Oxide

Classifying sedimentary rocks

• Two groups based on the source of the material 1. Detrital rocks (Residual solid material)

• Common rocks include• Shale (fine grained)

• Sandstone (medium grained)

• Conglomerate (round coarse grained)

• or Breccia (sharp coarse grain)

Classification of sedimentary rocks (page 59)

Shale with plant fossils

Sandstone

Conglomerate

Classifying sedimentary Rocks

2. Chemical Sedimentary rocks • Derived from material that was

once in solution and precipitates to form sediment. Two groups:

A – Chemical Organic Rocks

From biochemical processes; the most common sedimentary rocks:

Example: Limestone is the most abundant chemical rock .

• Coal: from plants-peat-bituminous coal-lignite-anthracite

Fossiliferous limestone

B - Chemical Inorganic rocks

Chemical Sedimentary RocksFrom precipitating solutions• Evaporites: Salt or gypsum rocks, • Through increase in concentration:

Hematite, chert, flint, jasper, or agate

Rock salt

Features of Sedimentary rocks

Features of sedimentary rocks• Strata, or beds (most characteristic)• Bedding planes separate stratas • Fossils

• Are traces or remains of prehistoric life

• Are the most important inclusions

• Help determine past environments

• Are used to determine age of sedimentary rocks

• Are used for rock correlation

PART – III: Metamorphic Rocks

FEEDBACK:

• What process forms metamorphic rocks?

• Where would you expect to find metamorphic rocks?

• Florida or Georgia? Why?

Metamorphic rocks

Are changed from other rocks, including other metamorphic rocks

• “Every metamorphic rock has a parent rock “

Metamorphism occurs between 200C – 800C at several kms depth

Causes and Types of metamorphism?

Heat from magma → Contact metamorphism

Pressure (stress) → Regional metamorphism• Confining pressure: from burial • Differential stress: during mountain building

• Chemically active fluids • Water and other volatiles (Hydrothermal fluids)

Types of pressure (stress) in metamorphism

Metamorphic Grades

Degrees of metamorphism

• Low-grade (where shale becomes slate)

• Medium-grade (where granite becomes gneiss)

• High-grade (rock partially melts → migmatite)

Metamorphic Textures

Nonfoliated from contact metamorphism

Typical rocks: Marble and Quartzite

Resembles a coarse-grained igneous rock

Is localized around intrusion

Marble – a Nonfoliated metamorphic rock

Development of foliation due to directed pressure

Gneiss typically displays a banded appearance

Classification of metamorphic rocks

Resources from rocks and minerals

Nonmetallic mineral resources • Make use of the material’s

• Nonmetallic elements

• Physical or chemical properties

• Two broad groups • Building materials (e.g., limestone, gypsum)

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

End of Chapter 3

1 - The Texture of an igneous rock is

a. Shape of the crystals

b. Size and arrangement of crystals

c. How hard of soft the rock feels

d. All of the above

e. I have no idea

2 – Texture of igneous rocks is determined by

a. Pressure and temperature

b. Amount of sulfur in the magma

c. Rate of cooling of magma

d. Depth of cooling of magma

e. c and d only

3 - The slower the rate of cooling,

the …a. Smaller the crystals of the rock

formed

b. Larger the crystals

c. No relation whatsoever

4 - Which terms characterize a basalt?

a. Felsic/Light colored/silica rich

b. Mafic/dark colored/silica poor

c. Felsic/dark colored/silica rich

d. Mafic/light colored/silica poor

5 - Name the volcanic rock (s)

a. Graniteb. Basaltc. Rhyolited. Gabbroe. b and c

6 - Is this rock:a: Plutonic? Or b: Volcanic?

7 – Porphyritic-aphanitic is what type of rock?

a. Plutonic with two rates of cooling

b. Volcanic with two rates of cooling

c. None of these

8 – Where to find a basaltic magma?

a. On the continental crust mainly

b. On the Oceanic crust

c. At the mid-ocean ridge

d. At subduction zone

e. b and c

9 –Which texture indicates a magma rich in gases?

a. Phaneritic

b. Aphanitic

c. Porphyritic

d. Pyroclastic

e. None of these

10 –Which texture indicates two rates of cooling?

a. Phaneritic

b. Aphanitic

c. Vesicular

d. Pyroclastic

e. None of these

11 – Where to find a felsic magma?

a. At mid ocean ridge

b. On the ocean floor

c. On the continental crust

d. At subduction zone

12 –Which term means fine-grained texture?

a. Aphanitic

b. Phaneritic

c. Porphyritic

d. Vesicular

e. None of these

13 - Texture?a: Glassy Or b: Pophyritic

14 - Which texture means all coarse-grained rock?

a. Aphanitic

b. Porphyritic

c. Phaneritic

d. Glassy

e. Vesicular

84

16 - Quartzite is what type of metamorphic rock?

a. Regional metamorphism

b. Contact metamorphism

c. Not a metamorphic rock

85

17 – In what type of metamorphism do pressure and temperature work

together?

a. Contact metamorphism

b. Regional metamorphism

c. All of the above

d. None of the above

86

18 - What is the parent rock of limestone?

a. Quartzite

b. Granite

c. Marble

d. Basalt

e. This does not make sense

87

19 – Which one of these is a foliated metamorphic rock?

a. Marble

b. Granite

c. Mica-schist

d. Basalt

e. Shale

20 -What type of weathering is frost wedging?

a. Chemical weathering

b. Mechanical weathering

c. Soil sampling

d. a and b

e. None of the above

a. Chemical weathering

b. Mechanical weathering

c. Soil sampling

d. a and b

e. None of the above

What type of weathering is oxidation?

22 - Exfoliation results from

a. Frost wedging

b. Oxidation

c. Unloading

d. Thermal expansion

e. None of the above

91

23 - Which one is the metamorphic rock?

Do not take

a. SANDSTONE for

b. GRANITE (granted)!

Have a

c. GNEISS (nice) day!

THE END

THAT’S ALL FOLKS!

THANK YOU!!!