Earth Materials

1
Chapter 2
Earth MaterialsMinerals and Rocks
2
Earth Materials Minerals

• Gemstones and other minerals,
• such as gold,
• have fascinated people for thousands of years
• and have been supposed
• to have mystical or curative powers
• Minerals have many essential uses
• in industrial societies
• Minerals are the basic units
• that make up most of Earths materials

3
Earth Materials Rocks

• With only a few exceptions rocks
• are solid aggregates of minerals
• Rocks too find many uses
• rocks crushed for aggregate in cement and for
  roadbeds
• sawed and polished rocks for tombstones,
• monuments, mantle pieces and counter tops
• Even the soils we depend on
• for most of our food
• formed by alteration of rocks

4
Minerals

• Geological definition of a mineral
• naturally occurring
• crystalline solid
• crystalline means that minerals
• have an ordered internal arrangement of their
  atoms

• minerals have a narrowly defined chemical
  composition
• and characteristic physical properties such as
• density
• hardness
• color...

5
Minerals

• Minerals on display
• at the California Academy of Sciences in San
  Francisco

6
Earth Materials

• Some materials formed by the Earth
• are interesting and attractive
• such as this metamorphic rock
• from the shoreline of Lake Superior at Marquette,
  Michigan

7
Matter and Its Composition

• Matter
• is anything that has mass and occupies space
• exists as solids, liquids, and gases
• consist of elements and atoms
• Element
• is a chemical substance
• that cannot be chemically decomposed
• into simpler substances
• and is composed of tiny particles called atoms

8
Atoms

• Atoms are the smallest units of matter
• that retain the characteristics of the element
• Atoms have
• a compact nucleus containing
• protons particles with a positive electrical
  charge
• neutrons electrically neutral particles
• particles orbiting the nucleus
• electrons negatively charged particles

9
Structure of an Atom

• The dense nucleus of an atom
• consisting of protons and neutrons
• is surrounded by a cloud of orbiting electrons

10
Atoms

• Atomic number
• the number of protons
• Atomic mass number
• number of protons number of neutrons
• The number of neutrons in an atom
• may vary

11
Isotopes

• The different forms of an elements atoms
• with varying numbers of neutrons
• are called isotopes.
• Different isotopes of the same element
• have different atomic mass numbers
• behave the same chemically
• Isotopes are important in radiometric dating

12
Carbon Isotopes

• Carbon atoms (with 6 protons)
• have 6 neutrons Carbon 12 (12C)

• have 7 neutrons Carbon 13 (13C)

• or have 8 neutrons Carbon 14 (14C)

• thereby making up three isotopes of carbon.

13
Electrons and Shells

• Electrons orbit the nucleus in one or more shells
• The outermost shell participates
• in chemical bonding
• and contains up to 8 electrons
• Noble gas configuration of 8 electrons
• or 2 for helium
• completes the outermost shell
• Other atoms attain
• a noble gas configuration
• in the process of bonding

14
Bonding and Compounds

• Bonding
• the process whereby atoms join to other atoms
• Compound
• a substance resulting from the bonding
• of two or more elements
• Oxygen gas (O2) is and element
• Ice is a compound
• made up of hydrogen and oxygen (H2O)
• Most minerals are compounds

15
Ionic Bonding

• Ion
• an atom that has gained or lost one or more
  electrons
• and thus has a negative or positive charge
• One way for atoms to attain the noble gas
  configuration
• is by transferring electrons, producing ions
• Ionic bonding
• attraction between two ions of opposite charge

16
Covalent Bonding

• Another way for atoms
• to attain the noble gas configuration
• is by sharing electrons

• Covalent bonding
• results from sharing electrons

shared electrons
17
MineralsThe Building Blocks of Rocks

• A minerals composition is shown by a chemical
  formula
• a shorthand way of indicating how many atoms of
  different kinds it contains

• Quartz consists of 1 silicon atom for every 2
  oxygen atoms

Quartz SiO2 Ratio 1 2

• Orthoclase consists of 1 potassium, 1 aluminum,
  and 3 silicon for every 8 oxygen atoms

KAlSi3O8 1 1 3 8
18
Native Elements

• A few minerals consist of only one element.
• They are not compounds.
• They are known as native elements.
• Examples

• gold formula Au

• diamond formula C

19
Crystalline Solids

• By definition, minerals are crystalline solids
• with atoms arranged in a specific 3D framework
• If given enough room to grow freely,
• minerals form perfect crystals with
• planar surfaces, called crystal faces
• sharp corners
• straight edges

20
Narrowly Defined Chemical Composition

• Some minerals have very specific compositions
• examples are halite (NaCl) or quartz (SiO2)
• but others have a range of compositions
• because one element can substitute for another
• if the atoms of the two elements have
• the same electrical charge
• and are about the same size
• example olivine
• (Mg,Fe)2SiO4
• iron and magnesium substitution in any proportion

21
Mineral Properties

• Mineral properties are controlled by
• Chemical composition
• Crystalline structure
• Mineral properties are particularly useful
• for mineral identification and include

• cleavage
• fracture
• hardness
• specific gravity

• color
• streak
• luster
• crystal form

22
Silicates

• Silicates are minerals containing silica
• Si and O
• They make up perhaps 95 of Earths crust
• and account for about 1/3 of all known minerals
• The basic building block of silicates
• is the silicon oxygen tetrahedron
• which consists of one silicon atom
• surrounded by four oxygen atoms

23
Types of Silicates

• Silica tetrahedra can be
• isolated units bonded to other elements
• arranged in chains (single or double)
• arranged in sheets
• arranged in complex 3D networks

24
Types of Silicates

• Ferromagnesian silicates (dark)
• contain iron (Fe), magnesium (Mg), or both
• Nonferromagnesian silicates (light)
• do not contain iron or magnesium

25
Ferromagnesian Silicates

• Common ferromagnesian silicates include

• augite, a pyroxene-group mineral

• olivine

biotite mica

• Hornblende, an amphibole-group mineral

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Nonferromagnesian Silicates

• Quartz Potassium feldspar
• Plagioclase feldspar Muscovite

27
Other Mineral Groups

• Carbonates
• minerals with carbonate ion (CO3)-2
• as in calcite (CaCO3),
• found in limestone

28
Rock-Forming Minerals

• Most rocks are solid aggregates
• of one or more minerals
• Thousands of minerals occur in rocks,
• but only a few are common
• and called rock-forming minerals
• Most rock-forming minerals are silicates,
• but carbonates are also important

29
Rock Cycle

• The rock cycle is a pictorial representation
• of events leading to
• the origin, destruction, change
• and reformation of rocks
• Rocks belong to 3 major families
• igneous
• sedimentary
• metamorphic
• The rock cycle shows
• how these rock families are interrelated
• and can be derived from one another

30
Rock Cycle
Lava
Pyroclastic material
31
Igneous Rocks

• All igneous rocks
• cool and crystallize from magma,
• solidify from lava,
• or consolidate from pyroclastic materials
• Magma is molten material
• below the surface
• Lava is molten material on the surface
• Pyroclastic materials
• are particles such as volcanic ash

32
Categories of Igneous Rocks

• Extrusive or volcanic rocks
• formed at the surface
• from lava or pyroclastic materials
• Intrusive or plutonic rocks
• formed from magma injected into the crust
• or formed in place in the crust
• Plutons are intrusive bodies
• consisting of plutonic rock

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Plutons
34
Igneous Rock Textures

• Texture
• is the size (coarse or fine)
• of crystals, grains and other constituents of a
  rock
• Igneous rocks have 4 textures
• that relate to cooling rate of magma or lava

35
4 Cooling-Rate Textures

• phaneritic,
• with visible grains
• cooled slowly
• aphanitic,
• with grains too small to see without
  magnification
• cooled quickly
• porphyritic,
• with larger grains surrounded by a finer-grained
  groundmass
• cooled slowly first, then more quickly
• glassy,
• with no grains
• cooled too quickly for minerals to grow

36
Igneous Rock Textures

• Other textures reveal further details
• of the formation of the rock
• Vesicular texture, with holes (vesicles),
• indicates the rock formed
• as water vapor and other gases
• became trapped during cooling of lava
• Pyroclastic or fragmental texture,
• containing fragments,
• formed by consolidation of volcanic ash
• or other pyroclastic material

37
Igneous Rock Textures

• Rapid cooling
• Aphanitic texture

• Slow cooling
• Phaneritic texture

• 2-stage cooling(mixed)
• Porphyritic texture

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Igneous Rock Textures

• Glassy texture
• cooling was too rapid for mineral growth

• Vesicular texture
• gasses trapped in cooling lava

• Pyroclastic texture
• particles fragmented during eruption

39
Classifying Igneous Rocks

• Texture and composition are the criteria
• used to classify most igneous rocks
• Composition categories are based on silica
  content or of light to dark minerals
  (non-ferromagnesian to ferromagnesian)
• felsic
• intermediate
• mafic
• More felsic magmas have higher Si, and higher Na,
  K, Al
• More mafic magmas have lower Si, and higher Ca,
  Fe, Mg

40
Classifying Igneous Rocks
41
Common Igneous Rocks

• Basalt

Gabbro
Andesite
Diorite
42
Common Igneous Rocks

• Rhyolite

Granite
43
Classifying Igneous Rocks with Special Textures
Vesicular Glassy Pyroclastic or Fragmental
Composition

• Texture

44
Igneous Rocks with Special Textures

• Tuff has pyroclastic texture.

Pumice is glassy and extremely vesicular.
45
Metamorphic Rocks

• Metamorphic rocks
• result from transformation of other rocks
• in the solid state, without melting
• Changes resulting from metamorphism
• compositional
• new minerals form
• textural
• minerals become reorientedfoliated
• minerals recrystallize
• or both

46
Agents of Metamorphism

• Heat provides new conditions
• where different minerals may be stable
• and increases the rate of chemical reactions
• Pressure
• Lithostatic pressure provides new conditions
• where different minerals may be stable
• and forms smaller denser minerals
• Differential pressure
• exerts force more intensely from one direction
• causing deformation
• and development of foliation.
• Fluid activity enhances metamorphism
• by increasing the rate of chemical reactions
• by transporting ions in solution

47
Types of Metamorphism

• Contact metamorphism
• heat
• chemical fluids
• from an igneous body
• alter rocks adjacent to the magma
• Regional metamorphism
• large, elongated area
• tremendous pressure
• elevated temperatures
• fluid activity
• occurs at convergent and divergent plate
  boundaries

48
Metamorphic Textures

• Foliated texture
• platy and elongate minerals aligned parallel to
  one another
• caused by differential pressure
• Nonfoliated texture
• mosaic of roughly equidimensional minerals
• or platy and elongate minerals
• arranged in a helter-skelter fashion
• with random orientations

49
Formation of Foliation

• When rocks are subjected to differential pressure
  (directional stress)
• the minerals typically rearrange or grow parallel
  to each other

50
Formation of Foliation

• Microscopic view
• of a metamorphic rock
• with foliation
• showing the parallel arrangement of minerals

51
Foliated Metamorphic Rocks

• Slate
• very fine-grained, breaks in flat pieces
• Phyllite
• fine-grained (coarser than slate but grains are
  still too small to see without magnification)
• breaks in flat pieces
• Schist
• clearly visible platy and/or elongate minerals
• Gneiss
• alternating dark and light bands of minerals

52
Nonfoliated Metamorphic Rocks

• Marble
• made of calcite or dolomite from limestone or
  dolostone
• Quartzite
• made of quartz from quartz sandstone
• Anthracite
• made of black lustrous carbon from coal
• Also Greenstone is a metamorphic rock associated
  with plate tectonics

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Common Metamorphic Rocks

• Slate

Schist
Gneiss
Marble
Quartzite