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Trace Evidence > Lecture 20 - Geology > Flashcards

Lecture 20 - Geology Flashcards

1
Q

what 7 things come under Forensic Geology

A

rocks
sediment
soil
dust
minerals
fossils
anthropogenic (concrete and bricks)

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2
Q

what is meant by an organic species

A

plant, animal or hydrocarbon based

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2
Q

what are sediments, soil and dust mixtures of

A

organic and inorganic particles

organic = shells, forams, phytoliths, diatoms, coal

inorganic = rock fragment, minerals, amorphous matter, glass

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3
Q

what other form of trace evidence looked at can be contained in rocks

A

diatoms e.g diatomaceous earth

made of diatoms, clay minerals and iron oxide

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3
Q

what are the three types of rock

A

igneous = from cooled liquid magma

metamorphic = formed due to variations in heat and pressure

sedimentary = from the accumulation of sediment

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3
Q

where are rocks often seen in casework - 2 ways

A

use of weights to sink things e.g bodies, weapons, drugs or as a projectile

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4
Q

where is diatomaceous earth found (7)

A

food
medicine
cosmetics
stabilising component in dynamite
pet litter
insulation
absorbents

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4
Q

what is the most prevalent rock type in forensics

A

sedimentary = approx 70% of earths surface

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5
Q

what are the 4 sediment types that make up rocks

how can we tell them apart

A

gravel
sand
silt
clay

by the particle size (descending order is above)

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5
Q

give three ways rocks and sediments are transported

A

air
water or ice
animals

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6
Q

where is gravel often found in casework (5)

A

tyre treads
shoe soles
victim mouths or respiratory tract
clothing
adhesive substances

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6
Q

what is shingle

A

a rounded gravel found in marine and lake environments

can be used in gardens for decorative purposes

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7
Q

when is geology evidence often used in forensics

A

to see if the location of victim death is where it was found

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8
Q

how big
a) gravel
b) cobbles
c) boulders

A

2mm - 64mm

cobbles = 64mm - 256mm
boulders = >256mm

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9
Q

where is sand often encountered in casework (2 locations)

where is sand likely to be found (6)

A

when a beach is involved
construction sites

footwear
clothing
vehicles
bodies
washing machine filters
u bend of sinks and toilets

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10
Q

how big are sand grains

A

0.063mm - 2mm

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11
Q

what is sand made of

A

many different minerals and rock fragments - mostly quartz = silicon dioxide

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12
Q

where is mud likely to be found in case work (5)

what locations is this likely to have come from (3)

A

on skin
fingernails
clothing
footwear
vehicles - tyres

floodplains
fields
woodland

13
Q

when is something classed as mud

A

a sediment that is sticky when wet

stickyness makes it persistent

14
Q

what is mud made of

A

mostly organic matter, mainly silt and clay with some sand and gravel

15
Q

how big are mud particles

A

<0.063mm

16
Q

why is soil good for suggesting locations

A

soils are very heterogenous and highly variable

they have distinct layers called horizons

16
Q

what things can impact soil formation (5)

A

climate = arid, dry, hot, cold
parent material
age
biological activity
soil type

17
Q

what are the three categories of things that make up soil - give some examples of each

A

non-living =
- inorganic material, salt crystals, decaying plant or animal matter, shells, insect exoskeletons, fossils, bones and teeth

living =
- bacteria, algae, fungi, plant roots, invertebrates, small mammals

unusual =
- cement, plaster, metal fragments, glass, paint flakes, fibres, plastic fragments

17
Q

what is the study of soil called

A

pedology

18
Q

what is
a) botany
b) palynology
c) ecology
d) palaeontology
the study of

A

a) plants
b) pollen
c) forams and diatoms
d) fossils

19
Q

what is the database used for soil samples

what does this allow

A

British Geological Survey - the UK Soil Observatory

can tell you where to find that particular make up of soil in the UK

19
Q

what varies in dust

what is dust indicative of

A

chemical composition

geographical area but they can be carried far as so small so bear that in mind

20
Q

how big are dust particles

A

<100 micrometre

21
Q

what is the most abundant type of minerals

name one other type

A

silicates - there are 6 classes

clay minerals = phyllosilicates

22
Q

what is a common use of clay minerals

A

in vermiculite

used for:
insulating material in fire resistance things,
concrete,
floor screed,
brake linings

so not always best for forensics as it also has commercial uses

22
Q

what are gemstones

A

minerals that are cut and polished to be used as jewellery or ornaments

23
Q

when is forensic gemology applied

what properties of gemstones are useful here (12)

A

in the analysis of counterfeits (fakes)

luminescence
fluorescence - some are naturally sluorescent
phosphorescence
birefringence
refraction
dispersion
hardness
magnetism
pleochroism
thermal conductivity
piezoelectricity
pyroelectricity

24
Q

what is
a) piezoelectricity
b) pyroelectricity

A

a) the analysis of electronic activity when applying pressure

b) the analysis of electronic activity when applying heat

25
Q

what type of assessment are we very unlikely to get here

A

physical fit as this evidence is mouldable to the surface it adheres to

25
Q

what are anthropogenic materials

A

man made - natural sources but have had human intervention

e.g
concrete
bricks
roof tiles
ceramic
plastic
fibres
paint
glass
metal

26
Q

what are the recovery considerations for soil sampls (6)

A

use a clean trowel for each layer, scrap the soil surface - don’t mix layers

look for footwear or tool impressions

screen soil samples for other evidence

take controls from suspected contact points

package each sample in separate bags - freeze to reduce change of bacteria/fungal growth

sketch showing areas sampled

27
Q

what is the analytical workflow for geology samples (soil) (12)

A
  1. gross examination, recovery and collection
  2. prelim evaluation of physical characteristics
  3. microscopic techniques
  4. MSP = colour determination
  5. pH and electrical conductivity measurements
  6. IR spectroscopy = organic content
  7. Raman = inorganic and carbon content
  8. SEM-EDX
  9. XRD = crystal structure, polymorphs
  10. AAS, XRF, ICP-AES = elemental composition
  11. isotopic analysis = look at isotope ratios
  12. chemometrics = HCA and PVA
28
Q

What microscopic techniques would be useful here

A

polarised light
SEM

29
Q

what are they two modes of SEM-EDX used here and for what

A

SE mode = surface topology

BSE mode = homogeneity

29
Q

why are soil samples suitable for MVA (multi variate analysis or chemometrics)

A

due to the large amount of samples to be compared

30
Q

what are some physical characteristics to note of samples here (8)

A

weight
volume
colour
texture
dimensions
surface area
perimeter
shape - sharpness, spherical

31
Q

which two charts produced by Munsell can be useful in colour determination here

A

soil colour chart
rock colour chart

Trace Evidence (16 decks)

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