Forensic Geology and Polarized Light Microscopy

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Forensic Geology and Polarized Light Microscopy
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Lewis Felts Case

• Location Front Royal, Va.
• Crime Homicide
• Evidence Soil on the
• suspects vehicle
• compared with soil from
• the crime scene at a river
• crossing.
• Samples contained
• Malachite and Azurite from an
• abandoned copper mine up
• stream.
• -soft copper minerals
• not found a short distance
• downstream.

Malachite light green/Cu2(CO3)(OH)2 Azurite
blue/Cu3(CO3)2(OH)2
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Eva Dirsch Case Crime Homicide

• In October of 1904 the strangled body of Eva
  Disch was found near Frankfurt, Germany
• When Georg Popp was called in he examined a
  filthy handkerchief found at the scene that
  contained bits of hornblende, snuff and, coal

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• As suspect Karl Laubach,used snuff, worked at the
  coal- burning local gas works and at a quarry
  that had hornblende bearing rocks
• The suspect also had mica in the cuffs of his
  trousers that matched mica at the murder scene

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Types of Microscopes
Stereo/Binocular Scope
Compound Microscope
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The Polarized Light Microscope -aka the PLM
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Physics of Light-The Basics
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Propagation of Light -modeled as descrete
particles photons -modeled as waves -in optical
microscopy we only consider the wave model
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f V/w f-frequency V-velocity of
light w-wavelength
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f V/w f-frequency V-velocity of
light w-wavelength f is nearly always constant,
therefore is V changes, w must change as well. n
(Refractive Index) c/v c-speed of light in
vacuum
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When light crosses boundary of 2 materials
with different refractive indices n, it is bent
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Refractive Index by the Becke Line Method
Note when refractive index of mineral liquid
are close, relief if low.
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GRIM 3 Glass Refractive Index Measurement
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Double-refraction in Calcite -the secret key
to PLM
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William Nicol Scottish Natural Philosophy
Professor -developed 1st Polarizing Prism in
1829 -took advantage of natural polarizing
nature of calcite.
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Polarizing Prism built by William Nicol
left Early PLM w/ Nicol Prism below
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Michel-Levy Chart of Birefringence
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Petrography PLM on a rock thinsection. -complime
ntary technique for grain liquid immersion
mounts -refractive index is more difficult to
determine -better for textures
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Quartz vein in cross-polarized Light -note 1st
order gray birefringence
Quartz vein in plane-polarized light
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Plagioclase Feldspar showing albite
twinning -used to determine Plagioclase
composition