The Chemistry of Geology

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The Chemistry of Geology
Minerals
Elements
Molecules
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Chemistry?!

• Geology is applied chemistry and physics
• Theres no way around it
• Basic knowledge is required to study Earth
  materials
• These are tools that geologists use to find out
  about what they are really interested in

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Rocks, minerals, and elements

• Rocks are a collection of one or more minerals
• Minerals are a collection of one or more elements

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Atoms
Positively charged protons and neutrally charged
neutrons make up the nucleus Negatively charged
electrons form a cloud in certain areas around
the nucleus Quantum effects abound! This is not
reality as we know it.
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Atoms

• Nucleus is massive and tiny
• Marble in a football field
• Greater than 99 of the weight
• Electrons have very little weight
• Zip around at high speeds
• Hang around in fixed areas (energy levels) called
  electron shells
• Electron shells can hold a fixed number of
  electrons

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Elements

• Elements are atoms, the basic building blocks of
  all materials
• Atoms cannot be broken down without nuclear
  reactions!
• All atoms are composed of various combinations of
  protons, neutrons, and electrons
• Protons, neutrons, and electrons are composed of
  even more particles
• These even more particles are composed of even
  more particles

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Elements

• The type of element is defined by the number of
  protons in the nucleus
• Hydrogen has 1 proton
• Carbon has 6 protons
• Iron has 26 protons
• Uranium has 92 protons

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The Periodic Table
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Common Elements in the Earth
Oxygen 45.2 Silicon 27.2 Aluminum 8.0 Iron 5.8 C
alcium 5.1 Magnesium 2.8 Sodium 2.3 Potassium 1.7
Titanium 0.9
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Isotopes!

• The number of neutrons in an element can vary
• The chemical properties remain the same
• The only difference is the atomic mass

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Isotopes

• Chemical reactions proceed at different rates
  depending on the isotope
• e.g. 13C/12C, 18O/16O, 238U/235U
• Some isotopes can be unstable and decay into more
  stable elements
• 14C ? 14N

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Uses For Stable Isotopes

• Past climates Ocean temperatures from forams
  (18O)

Tiny sea critter shells
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Uses For Stable Isotopes

• Biological signatures 13C

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Uses for Unstable Isotopes

• How old is it?
• Isotopes decay at a very predictable rate
• Example - 14C dating of organic material

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Chemical Bonding

• Atoms like to have complete electron shells
• They can do this by either losing, gaining, or
  sharing electrons with other elements

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How do different elements bond?
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Ionic Bonds

• One atom loses electrons, another atom gains
  electrons
• Opposite charges hold atoms together
• Example Salt - Sodium (Na) and Chlorine (Cl)

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Ionic Bonds

• Often dissolve in water
• Because of ionic (charged) nature of H2O
• Opposite charges of ions (e.g. Na Cl-) holds the
  elements together in an orderly fashion
• e.g. alternating pattern of Na and Cl-

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Ionic Bonds

• Sodium Chloride a.k.a. NaCl a.k.a salt

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Covalent Bonds

• Covalent bonds occur when atoms share electrons
• Monatomic gasses such as O2, N2, Cl2
• Solids such as silicates (SiO2)
• Electron shells overlap and electrons hang out in
  area common to both electron shells

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Even More Bonds

• Ionic/Covalent hybrid bonds
• Many substances have something in-between the two
  bond types
• Metallic bonds
• Electrons are free to roam through the material
• Accounts for conductivity, malleability, etc

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Crystal Structure
Crystal structure depends on both ion charge and
atom size Atom size is in angstroms 10-8 cm
0.00000001 cm
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Crystal Structure

• Minerals often reflect their crystal structure
• Once again, salt is a good example

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Polymorphs

• Two or more minerals with the same chemical
  composition but different crystal structure
• Transformation from one polymorph to another is
  called a phase change
• e.g. graphite and diamonds are both composed of
  carbon
• Polymorphs can indicate pressure and temperature
  conditions under which the mineral formed

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Cliffhanger!

• How is it that these elements arrange each other
  into minerals?!?!
• Find out next time