Lecture 20 - Geology Flashcards
what 7 things come under Forensic Geology
rocks
sediment
soil
dust
minerals
fossils
anthropogenic (concrete and bricks)
what is meant by an organic species
plant, animal or hydrocarbon based
what are sediments, soil and dust mixtures of
organic and inorganic particles
organic = shells, forams, phytoliths, diatoms, coal
inorganic = rock fragment, minerals, amorphous matter, glass
what other form of trace evidence looked at can be contained in rocks
diatoms e.g diatomaceous earth
made of diatoms, clay minerals and iron oxide
what are the three types of rock
igneous = from cooled liquid magma
metamorphic = formed due to variations in heat and pressure
sedimentary = from the accumulation of sediment
where are rocks often seen in casework - 2 ways
use of weights to sink things e.g bodies, weapons, drugs or as a projectile
where is diatomaceous earth found (7)
food
medicine
cosmetics
stabilising component in dynamite
pet litter
insulation
absorbents
what is the most prevalent rock type in forensics
sedimentary = approx 70% of earths surface
what are the 4 sediment types that make up rocks
how can we tell them apart
gravel
sand
silt
clay
by the particle size (descending order is above)
give three ways rocks and sediments are transported
air
water or ice
animals
where is gravel often found in casework (5)
tyre treads
shoe soles
victim mouths or respiratory tract
clothing
adhesive substances
what is shingle
a rounded gravel found in marine and lake environments
can be used in gardens for decorative purposes
when is geology evidence often used in forensics
to see if the location of victim death is where it was found
how big
a) gravel
b) cobbles
c) boulders
2mm - 64mm
cobbles = 64mm - 256mm
boulders = >256mm
where is sand often encountered in casework (2 locations)
where is sand likely to be found (6)
when a beach is involved
construction sites
footwear
clothing
vehicles
bodies
washing machine filters
u bend of sinks and toilets
how big are sand grains
0.063mm - 2mm
what is sand made of
many different minerals and rock fragments - mostly quartz = silicon dioxide
where is mud likely to be found in case work (5)
what locations is this likely to have come from (3)
on skin
fingernails
clothing
footwear
vehicles - tyres
floodplains
fields
woodland
when is something classed as mud
a sediment that is sticky when wet
stickyness makes it persistent
what is mud made of
mostly organic matter, mainly silt and clay with some sand and gravel
how big are mud particles
<0.063mm
why is soil good for suggesting locations
soils are very heterogenous and highly variable
they have distinct layers called horizons
what things can impact soil formation (5)
climate = arid, dry, hot, cold
parent material
age
biological activity
soil type
what are the three categories of things that make up soil - give some examples of each
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
what is the study of soil called
pedology
what is
a) botany
b) palynology
c) ecology
d) palaeontology
the study of
a) plants
b) pollen
c) forams and diatoms
d) fossils
what is the database used for soil samples
what does this allow
British Geological Survey - the UK Soil Observatory
can tell you where to find that particular make up of soil in the UK
what varies in dust
what is dust indicative of
chemical composition
geographical area but they can be carried far as so small so bear that in mind
how big are dust particles
<100 micrometre
what is the most abundant type of minerals
name one other type
silicates - there are 6 classes
clay minerals = phyllosilicates
what is a common use of clay minerals
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
what are gemstones
minerals that are cut and polished to be used as jewellery or ornaments
when is forensic gemology applied
what properties of gemstones are useful here (12)
in the analysis of counterfeits (fakes)
luminescence
fluorescence - some are naturally sluorescent
phosphorescence
birefringence
refraction
dispersion
hardness
magnetism
pleochroism
thermal conductivity
piezoelectricity
pyroelectricity
what is
a) piezoelectricity
b) pyroelectricity
a) the analysis of electronic activity when applying pressure
b) the analysis of electronic activity when applying heat
what type of assessment are we very unlikely to get here
physical fit as this evidence is mouldable to the surface it adheres to
what are anthropogenic materials
man made - natural sources but have had human intervention
e.g
concrete
bricks
roof tiles
ceramic
plastic
fibres
paint
glass
metal
what are the recovery considerations for soil sampls (6)
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
what is the analytical workflow for geology samples (soil) (12)
- gross examination, recovery and collection
- prelim evaluation of physical characteristics
- microscopic techniques
- MSP = colour determination
- pH and electrical conductivity measurements
- IR spectroscopy = organic content
- Raman = inorganic and carbon content
- SEM-EDX
- XRD = crystal structure, polymorphs
- AAS, XRF, ICP-AES = elemental composition
- isotopic analysis = look at isotope ratios
- chemometrics = HCA and PVA
What microscopic techniques would be useful here
polarised light
SEM
what are they two modes of SEM-EDX used here and for what
SE mode = surface topology
BSE mode = homogeneity
why are soil samples suitable for MVA (multi variate analysis or chemometrics)
due to the large amount of samples to be compared
what are some physical characteristics to note of samples here (8)
weight
volume
colour
texture
dimensions
surface area
perimeter
shape - sharpness, spherical
which two charts produced by Munsell can be useful in colour determination here
soil colour chart
rock colour chart
