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Earth and Ocean Systems > Chemistry, Geochemistry, Minerals & Rocks > Flashcards

Chemistry, Geochemistry, Minerals & Rocks Flashcards

Lectures 3.1-3.5

1
Q

What is a crystal?

A
  • Homogenous solid formed by repeating 3D patterns of atoms, ions or molecules
  • Most of solid earth
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2
Q

What is a molecule?

A

Group of 2 or more of the same or different elements held together by chemical bonds. Electrically neutral.

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3
Q

What is a mineral?

A

Element or chemical compound, usually crystalline and formed via a geological process.

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4
Q

What is a group number?

A

Number of electrons in outermost shell.

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5
Q

What is the period number?

A

Number of shells.

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6
Q

What are valence electrons?

A

Number of electrons available for bonding.

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7
Q

What is the importance of transition metals?

A
  • Can exist in variable oxidation states
  • Donates or accept electrons easily
  • Able to bond to a wide range of molecules/ions
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8
Q

What is ionisation energy?

A
  • Energy to remove least strongly bound electron, creating a positively charged cation.
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9
Q

What is electronegativity?

A
  • Ability of bonded atom to pull electrons
  • Become a negatively charged ions
    -Increases from the bottom left of the periodic table
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10
Q

Describe ionic bonds.

A

One or more electrons from one atom are taken, attached to another atom. Results in + and - ions that attract eachother.

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11
Q

Describe a covalent bond.

A

One or more pairs of electrons are shared by to atoms. Can be polar or non polar. This is what water uses as O has a higher attraction for electrons, as it is more electronegative.

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12
Q

Describe Van de Waals forces.

A
  • Weak
  • Due to a permanent dipole, a multiple multipole or spontaneously induced dipole
  • Important for things like graphite
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13
Q

What is the importance of electronegativity in chemical bonding?

A
  • As electronegativity increases:
    Covalent non polar to
    Covalent polar to
    Ionic
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14
Q

Describe metallic bonds.

A
  • Electrons in certain orbits are detached from parent atoms
  • Metal bound by strong attraction between positive nuclei and de-localised electrons
  • Hence ability to conduct electricity
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15
Q

Describe hydrogen bonds.

A
  • Attraction between H atom and atom of high electronegativity (mostly N,O or F)
  • In water, proteins and DNA
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16
Q

Who recognised a partitioning of elements according to their preferred host phases?

A

Victor Goldschmidt.

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17
Q

Describe the 4 partitioning of elements?

A

Atmophile: Volatile, form mainly atmospheric gases
Lithophile: Silicates and oxides - rock forming and dominate crust/mantle.
Chalcophile: Affinity for sulfide liquid phase
Siderophile: Affinity for metallic liquid phase

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18
Q

How did oxygen amounts determine the lithophile layer?

A

Used up all of the oxygen after all Si, Mg, Ca and Al were used up. So was just based on what was left.

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19
Q

How are minerals separated?

A

The principle ion (negative ion)
or
Anionic Group (negative molecule)

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20
Q

How does the environment in which carbon cools determine the polymorph it ends up as?

A
  • Diamond: Each C bound to 4 other C via covalent bonds.
    Graphite: Each C bonded to 3 other C, spare electron is delocalised. This also has Van de Waals forces.
21
Q

How do we view inside crystals?

A
  • X ray diffraction usually
    But also electron microscopy can be used
22
Q

How do we use TEMs to view inside crystals?

A
  1. Shoot a beam of electrons at a crystal
  2. Electrons pass through spaces, reaching a detector
  3. Electrons interacting with atoms don’t reach detector
  4. Dark and light pattern images crystal atoms
23
Q

Describe the mineral class: Oxides

A
  • Metal cations bonded to oxygen
  • Includes magnetite
24
Q

Describe the mineral class: Sulphides

A
  • Metal cations bonded to sulfide anion
  • Includes pyrite
25
Q

Describe the mineral class: Sulphates

A
  • Metal cation bonded to sulphate anionic group
  • Includes gypsum
  • Often evaporite deposits
26
Q

Describe the mineral class: Halides

A
  • Cl⁻ or F⁻
  • Includes Halite
  • Often evaporite deposits
27
Q

Describe the mineral class: Carbonates

A
  • CO₃²⁻
  • Includes calcite and dolomite
28
Q

What are native elements?

A

Pure masses of a single metal, such as gold.

29
Q

Describe silicate mineral structure.

A
  • SiO₄⁴⁻ : Silicon oxygen tetrahedron
  • 4 O atoms bonded to Si
  • Define corners of 4 sided geometric figure
  • Divided into groups based on ratio of Si:O (important for melting temperature, mineral structure, susceptibility to chemical weathering, cations present)
30
Q

What are silicate independent tetrahedra?

A
  • Si:O = 1:4
  • Share no oxygens
  • Linked by cations
  • Include garnet
31
Q

What are single chain silicate minerals?

A
  • Si:O = 1:3
  • One shares two oxygens
  • Pyroxenes
32
Q

What are framework silicate minerals?

A
  • Si:O = 1:2
  • All 4 oxygens in each tetrahedra are shared
  • Include feldspars and silica
33
Q

What are sheet silicate minerals?

A
  • Si:O = 2:5
  • Silica tetrahedra share 3 oxygens
  • Create 2D flat sheets of tetrahedra
  • One direction of perfect cleavafe
  • Include Micas like biotite and Clays
34
Q

How does the melting of the continental crust create magma and its residue?

A
  • When melting, only a portion of the rock melts. Si rich minerals melt first, so a partial melt creates:
  • Felsic magma
  • Mafic residue
35
Q

What did N.L.Bowen experiment and find out?

A
  • Experimented cooling melts, with the remaining melt being enriched in Si, Al % Na.
  • He discovered minerals solidify in a specific series.
36
Q

What are the two types of mineral solidification?

A

Continuous: Plagioclase (Al rich mineral in mafic rocks) changed from Ca to Na rich.
Discontinuous: Minerals start and stop crystallising.

37
Q

How are metamorphic rocks created?

A
  • Plate tectonic collisions that thicken the crust
  • Create new minerals as shearing field rocks. These are then exposed by uplift and erosion.
  • side note, this liberates CO2.
38
Q

Define weathering.

A

Disintegration and decomposition of rocks and sediments mechanically or chemically in situ.

39
Q

Define erosion.

A

Process in which primarily rock or soil are detached and transported by weather.

40
Q

Describe frost wedging.

A
  • Rain goes into crack
  • Crack freezes and therefore expands
  • Rock break
41
Q

Describe Salt Wedging.

A
  • Salt water gets into rock
  • Dries, salt crystals expand
  • Rock break
42
Q

Describe Thermal expansion and contraction.

A
  • Minerals and expand and contract due to extreme diurnal temperature ranges
43
Q

Describe exfoliation.

A
  • Spalling (removal) of surface layers
  • Due to release of lithostatic pressure and expansion as rock is exhumed
  • Due to chemical + physical weathering
44
Q

Describe root wedging.

A

Biological weathering. Just roots in a joint growing.

45
Q

Describe abrasion.

A

Wind action.

46
Q

Describe dissolution.

A
  • Reaction between minerals and acidic/alkaline water (mostly slightly acidic rainwater)
  • Dissolves calcite in limestone
  • Known as carbonation
  • Also some is caused just by polarity of water
47
Q

Describe Hydration weathering.

A

Absorption of water.
- Example being Anhydrite (CaSO⁴) accepts water to become gypsum.

48
Q

Describe Hydrolysis.

A
  • Reaction between H+ and OH- ions of water and the mineral.
  • With silicate this is a negative feedback cycle as silicate weathering consumes CO2 which cools the climate and decreases chemical weathering.
49
Q

What are the effects of metamorphism and volcanism have on CO2?

A

Metamorphism - liberates CO2
Volcanism - Releases Co2

Earth and Ocean Systems (5 decks)

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