1. 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

2. Forensic Geology The legal application of earth and soil science
Almost always an issue of “transfer”
Can be individualized under the right circumstances

3. Forensic Geology Important Forensic properties Mineral content
Rock content
Plant matter
Animal matter
Artificial material

4. Forensic Geology Uses Vehicle Accidents Rape/Assault Burglary
Vehicles frequently strike natural objects
Rape/Assault
Can be useful if crime occurs outdoors
Burglary
Properties often have flowerbeds, etc. beneath common entry points

5. 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
First manual included the study of “dust, dirt on shoes and spots on cloth”
“Dirt on shoes can often tell us more about where the wearer of those shoes had last been than toilsome inquiries.”
-Hans Gross

6. 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

7. What is Forensically Valuable?
Unusual mineral/rock components
Fossils
Man-made components
Color of material

8. Geologic Terminology Geology Mineralogy Petrology Paleontology
The study of the Earth and its processes
Mineralogy
Study of minerals
Petrology
Study of rocks
Paleontology
Study of the Earth’s past

9. 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

10. Minerals and Rocks Rock An group of minerals combined together
Each mineral found in the rock keeps its original properties
A few rocks contain only one primary mineral (calcite – limestone)

11. Minerals and Rocks Rocks come in three major types Igneous Sedimentary
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

12. 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

13. 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

14. 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

15. Forensic Mineralogy Essentials
Density
Determined by relative chemical composition and closeness of atoms in crystal
Most rock forming minerals: g/cm3
Most metallics: >5.0 g/cm3

16. Forensic Mineralogy Essentials
Luster
Appearance of reflected light from the surface of the mineral
Main classifications are metallic and non-metallic
Non-metallic subcategories
Glassy
Resinous
Fibrous
Waxy
Earthy/dull
Brilliant
Pearly

17. Forensic Mineralogy Essentials
Color
Not a reliable property since small impurities can change color (Corundum)
Only a few minerals occur in one color
General guesses about composition can be made based on colors
Dark (black, greys, greens, etc.) - contain metals, Fe
Light (tans, clears, reds) - contain Si or Al

18. Forensic Mineralogy Essentials
Streak
Color of the mineral in a powdered form
Found by rubbing the mineral across a streak plate
Streak the same regardless of mineral color differences
Reliable for hardnesses of ~7 or less

19. Forensic Mineralogy Essentials
Quartz
A glassy, hard crystal
Often looks like broken glass
Can appear in many colors
Will easily scratch glass

20. Forensic Mineralogy Essentials
Feldspar
Fleshy appearance
Slightly softer than quartz
Will often have up to 4 flat sides

21. Forensic Mineralogy Essentials
Mica
Very soft – usually found in flakes
Flat and shiny
Has two varieties
1 – Coppery color (more common)
2 – Gloss black

22. Forensic Mineralogy Essentials
Calcite
Chief mineral in limestone
Glassy to white blocky crystals
Slightly harder than a fingernail
Will fizz in HCl

23. Forensic Mineralogy Essentials
Hornblende and Pyroxene
Hard, dark (dk. Green to black) minerals
Almost always blocky
Unusual in most settings

24. Forensic Petrology Essentials
Granite
Most common igneous rock
Combination of light and dark minerals discussed earlier

25. Forensic Petrology Essentials
Sandstone (sed.) and quartzite (meta.)
Typically quartz and feldspar combo.
Looks like sand
Quartzite will have similar color but sand grains will be smashed/fused together

26. Forensic Petrology Essentials
Limestone (sed.)
Limestone is almost always a shade of grey
Will fizz with HCl or vinegar
Metamorphic version is marble (uncommon)
Also look for calcite veins – limestone is composed of calcite

27. Forensic Petrology Essentials
Shale (sed.) and slate (meta.)
Very smooth appearance
Obvious layering
Usually dark grey but also brick red or olive green
Shale is very brittle
Slate will be same color but not brittle

28. Forensic Petrology Essentials
“Sand”
Caution should be taken when using this term
“Sand” is a general term that describes grain size, not specific mineral content
Gravel > > Sand > > Silt > > Clay

29. 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

30. 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”

31. 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