Title: Forensic Geology and Polarized Light Microscopy
1Forensic Geology and Polarized Light Microscopy
2Lewis 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
3Eva 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
4- 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
5Types of Microscopes
Stereo/Binocular Scope
Compound Microscope
6The Polarized Light Microscope -aka the PLM
7Physics of Light-The Basics
8Propagation of Light -modeled as descrete
particles photons -modeled as waves -in optical
microscopy we only consider the wave model
9f V/w f-frequency V-velocity of
light w-wavelength
10f 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
11When light crosses boundary of 2 materials
with different refractive indices n, it is bent
12(No Transcript)
13(No Transcript)
14Refractive Index by the Becke Line Method
Note when refractive index of mineral liquid
are close, relief if low.
15GRIM 3 Glass Refractive Index Measurement
16Double-refraction in Calcite -the secret key
to PLM
17(No Transcript)
18William Nicol Scottish Natural Philosophy
Professor -developed 1st Polarizing Prism in
1829 -took advantage of natural polarizing
nature of calcite.
19Polarizing Prism built by William Nicol
left Early PLM w/ Nicol Prism below
20(No Transcript)
21Michel-Levy Chart of Birefringence
22(No Transcript)
23Petrography PLM on a rock thinsection. -complime
ntary technique for grain liquid immersion
mounts -refractive index is more difficult to
determine -better for textures
24(No Transcript)
25Quartz vein in cross-polarized Light -note 1st
order gray birefringence
Quartz vein in plane-polarized light
26Plagioclase Feldspar showing albite
twinning -used to determine Plagioclase
composition