Halito!

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Halito!

• Do Now
• pick up two handouts
• Turn in lab book on side bench by windows
• Agenda
• X-ray Diffraction
• reading spectra
• HW
• Finish handout

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X-ray Diffraction (XRD) and Forensic Geology
X-ray diffraction pattern for goethite
X-ray diffractometer (XRD) laboratory
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Structure of minerals

• Minerals consist of an orderly array of atoms
  chemically bonded to form a particular
  crystalline structure.
• Internal atomic arrangement in ionic compounds is
  determined by ionic size.

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What is X-Ray Diffraction??

• Crystalline substances (e.g. minerals) consist of
  parallel rows of atoms separated by a unique
  distance
• Simple Example
• Halite (Na and Cl)

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Geometric packing of various ions
Figure 3.8
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Structure of Minerals

• Crystal Lattice the three dimensional molecular
  structure of a mineral. (Shape of the unit
  cell.)
• the various ions that make up the mineral.
• Crystalline substances consist of parallel rows
  of atoms separated by a unique distance

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Structure of Minerals
Halite (rock salt)
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X-Rays
Wavelengths used for XRD
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• Crystalline substances (e.g. minerals) consist of
  parallel rows of atoms separated by a unique
  distance
• Diffraction occurs when radiation enters a
  crystalline substance and is scattered
• Direction and intensity of diffraction depends on
  orientation of crystal lattice with radiation

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Braggs Law ? 2d(sin?) where ? x-ray
wavelength d spacing between planes of atoms
in crystal sin ? x-ray incidence angle (Bragg
angle) also d ? /2sin ? sin ? ? /2d
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Sample XRD Pattern
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