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									Trace Evidence 1
    Forensic Geology

                   “Life is hard. Then you die.
   Then they throw dirt in your face. Then the
                                worms eat you.
          Be grateful it happens in that order.”
                                    —David Gerrold
           Forensic Geology
 The legal application of
  earth and soil science
 Almost always an issue
  of “transfer”
   earth materials that have
    been transferred
    between objects or
    locations and their origins
 Can be individualized
  under the right
  circumstances
         Forensic Geology
Important Forensic properties
  Mineral content
  Rock content
  Plant matter
  Animal matter
  Artificial material
     Forensic Geology Uses
Vehicle Accidents
  Vehicles frequently strike natural objects
Rape/Assault
  Can be useful if crime occurs outdoors
Burglary
  Properties often have flowerbeds, etc.
   beneath common entry points
   History of Forensic Geology
 1887–1893
   Sir Arthur Conan Doyle
   Several Sherlock Holmes cases
    suggested the possible use of soil
    in criminal investigations
 1893
   Hans Gross Considered to be the
    first criminalist
                                         “Dirt on shoes can
   First manual included the study of   often tell us more about
    “dust, dirt on shoes and spots on    where the wearer of
                                         those shoes had last
    cloth”                               been than toilsome
                                         inquiries.”
                                         -Hans Gross
 History of Forensic Geology
 1910
   Edmond Locard
   Was interested in the fact
    that dust was transferred
    from the crime scene to
    the criminal
     Helped to establish his
      Exchange Principle



                                 Edmond Locard
 What is Forensically Valuable?

Unusual
 mineral/rock
 components
Fossils
Man-made
 components
Color of material
     Geologic Terminology
Geology
  The study of the Earth and its processes
Mineralogy
  Study of minerals
Petrology
  Study of rocks
Paleontology
  Study of the Earth’s past
        Minerals and Rocks
To be considered a mineral, 5
 requirements must be met
  Naturally occurring
  Inorganic (Exception: material formed by
   the activity of animals...pearls)
  Solid
  Definite chemical structure which provides
   for specific physical properties
  Recurring atomic structure (crystal)
~4000 exist but only a few dozen are
 found in large quantities
        Minerals and Rocks
Rock
 An aggregate of minerals
 Each mineral found in the rock retains its
  original properties
 A few rocks contain only one primary
  mineral (calcite - limestone)
 Largely identified by physical
  appearance rather than specific physical
  properties
       Minerals and Rocks
Rocks come in three major types
Igneous
  The direct result of volcanic processes
Sedimentary
  The result of weathering and erosion of
   other rocks
Metamorphic
  The result of intense heating or pressure of
   other existing rocks
Mineral and Rock Identification
Minerals are largely identified by
 specific physical and chemical
 properties
Rocks are largely identified by
 physical appearance
  Properties can vary since there’s no
   specific “formula” for a rock
  Example: Granite
Mineral and Rock Identification
Geologic Setting
  The sum total of geologic conditions (past
   and present) for a particular area
  Absolutely essential in any geologic
   investigation
  Greatly assists in including or eliminating
   possible geologic “species”
Mineral and Rock Identification
In general (not considering geologic
 setting)
  Quartz is the most common mineral on
   Earth
  Most earth samples will contain only 3-5
   different minerals and rocks
  75% of anything picked up will be a
   sedimentary rock
Forensic Mineralogy Essentials
Among the most useful and reliable of
 properties
Mohs Scale
  Used as a standard
  1-10
Field Hardness Scale
  Uses approximations of common items
    Fingernail = 2.5
    Penny = 3
    Glass = 5.5
    Steel = 7
Forensic Mineralogy Essentials
Specific Gravity
  Determined by relative chemical
   composition and closeness of atoms in
   crystal
Most rock forming minerals: 2.0 - 3.0
 g/cm3
Most metallics: >5.0 g/cm3
Forensic Mineralogy Essentials
 Luster
   Appearance of reflected light from the surface of
    the mineral
   Main classifications are metallic and non-
    metallic
 Non-metallic subcategories
   Vitreous (glassy)
   Resinous
   Silky (fibrous)
   Waxy
   Earthy (dull)
   Adamantine (brilliant)
   Pearly
Forensic Mineralogy Essentials
Color
  Not a reliable property since small
   impurities can change color (Corundum)
  Only a few minerals occur in one color
   only (galena, sulfur, azurite, etc.)
General guesses about composition
 can be made based on relative colors
  Dark (black, greys, greens, etc.) - contain
   metals, Fe
  Light (tans, clears, reds) - contain Si or Al
Forensic Mineralogy Essentials
Streak
  Color of the mineral in a powdered form
  Found by rubbing the mineral across a
   hard unglazed porcelain streak plate
  Streak generally the same regardless of
   mineral color differences
  Reliable for hardnesses of ~7 or less
Forensic Mineralogy Essentials
 Luminescence
   The emission of light
    as a result of stress
   Fluorescence - will
    disappear after
    energy source is
    removed
   Phosphorescence -
    will remain for awhile
    after energy source
    is removed
Forensic Mineralogy Essentials
Quartz
 A glassy, hard crystal
 Often looks like broken glass
 Can appear in many colors
 Will easily scratch glass
Forensic Mineralogy Essentials
Feldspar
  Fleshy appearance
  Slightly softer than quartz
  Will often have up to 4 flat sides
Forensic Mineralogy Essentials
Mica
 Very soft – usually found in flakes
 Flat and shiny
 Has two varieties
 1 – Coppery color (more common)
 2 – Gloss black
Forensic Mineralogy Essentials
Calcite
  Chief mineral in limestone
  Glassy to white blocky crystals
  Slightly harder than a fingernail
  Will fizz in HCl
Forensic Mineralogy Essentials
Hornblende and Pyroxene
 Hard, dark (dk. Green to black) minerals
 Almost always blocky in appearance
 Unusual in most geologic settings
 Forensic Petrology Essentials
Granite
  Most common igneous rock
  Combination of light and dark minerals
   discussed earlier
 Forensic Petrology Essentials
Sandstone (sed.) and quartzite (meta.)
  Sandstone is typically a combination of
   quartz and feldspar
  Looks like sand
  Quartzite will have similar color but sand
   grains will be smashed/fused together
 Forensic Petrology Essentials
Limestone (sed.) and dolostone (sed.)
  Limestone is almost always a shade of
   grey
  Will vigorously react with HCl
  Dolostone will look the same but only
   react slightly
  Metamorphic version is marble
   (uncommon)
  Also look for calcite veins – limestone is
   composed of calcite
 Forensic Petrology Essentials
Shale (sed.) and slate (meta.)
  Very smooth appearance
  Obvious layering
  Usually dark grey but also brick red of
   olive green
  Shale is very brittle
  Slate will be same color but not brittle
 Forensic Petrology Essentials
“Sand”
 Caution should be taken when using this
  term
 “Sand” is a generic geology term that
  describes grain size, not specific mineral
  content
Gravel
Sand
Silt
Clay
 Forensic Petrology Essentials
Siltstone (sed.)
  Similar to sandstone but smaller particles
  Often mica-rich (look for the “shine”)
  Very soft and brittle
  Usually a stream deposit
      UD Geologic Setting
Light colored minerals are common
  Quartz, feldspar and micas
Micas especially common in stream
 gravels/sands
Most rocks will be sedimentary or their
 metamorphic versions
  Sandstone, limestone shale are common
Many artificially introduced
 minerals/rocks

								
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