Pigments in Forensic Geology

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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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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.
• Geometry chemistry!

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Structure of Minerals
Halite (rock salt)
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Diagram illustrating Braggs law. ? angle of
incidence and diffraction when Braggs law
conditions are met. d inter-planar spacing.
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Braggs Law ? 2d(sin?) where ? x-ray
wavelength d spacing between planes of atoms
in crystal ? ? x-ray incidence angle (Bragg
angle) also d ? /2sin ? sin ? ? /2d
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XRD Laboratory
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