Advanced Evidence Types Flashcards
What are the 7 kinds of forensic geology?
What can be said about 3/7 of these?
rocks
sediments
soils
dusts
minerals
fossils
anthropogenic e.g. concrete, bricks
sediments soils and dust are mixtures of organic/inorganic particles where
- organic fractions (hydrocarbon based, plant/animal based) derive from: biological processes, e.g. shells and forams (calcite, aragonite), phytoliths (silica), diatoms, or CHO based products (e.g. coal)
- inorganic fractions include rock fragments, mineral grains and amorphous matter, e.g. volcanic glass
When are rocks encountered in forensic casework?
- weights to sink bodies
- in bags containing illicit substances/firearms
- as concealment material in smuggling cases
- as projectiles (thrown or catapulted
What are three main classifications of rocks?
Which one is most interested in as forensic perspective?
- igneous - rocks formed from liquid magma cooled deep in the earth or extruded onto surface by volcanos
- metamorphic - rocks formed by varying degrees of heat and pressure on any type of existing rock
- sedimentary - rocks formed by accumulation of sediment in water and air by processes of erosion, precipitation, evaporation and compaction
- sedimentary - around 70 % of earths surface
What is diatomaceous earth?
- predominantly made of 80-90 % diatoms (silica) aluminium oxide if forms of clay minerals, iron oxide
- diatoms are useful form of TE
- if diatomaceous earth in rocks, got something useful to look at
- it is in food, medicines, cosmetics, absorbents, insulating materials, pet litter, even as a stabilising component in dynamite – chances of finding it are pretty high
What are sediments and what makes them different to rocks?
What are four main categories of sediment?
- particle mixtures from a variety of sources, transported and deposited by air, water or ice
- this makes sediments distinct from rock
- gravel
- sand
- silt
- clay
Define gravel
- when encountered
- size discrimination
- rounded gravel
- encountered in casework in tyre treads, shoe soles, in drowning victim’s mouths/respiratory tract/clothing (in pockets/hoods/shoes), or on associated adhesive tapes (gagged or bound)
- size discrimination:
- gravel = 2 mm – 64 mm
- cobbles = 64 mm – 256 mm
- boulders = >256 mm
- shingle = rounded gravel
- found in driveways, flowerbeds, decorative reasons
- also found in marine and lake environments because water is constantly eroding surface
Define sand
- when encountered
- size discrimination
- for a sediment to be classed as sand…
- what is it made up of
- encountered in casework involving beaches, sand dunes, and construction sites;
- found on/in footwear, clothing, vehicles, bodies, washing machine filters and U-bends of sinks and toilets (because it sediments)
- when flush toilet or wash garments with sand – particles will be trapped
- size discrimination:
- sand grains = 0.063 mm – 2 mm
- for a sediment to be classed as sand it must contain >50% sand grain sized particles otherwise gravel or something else
- made up of many different minerals – rock fragments (lithic grains) – predominantly quartz
Define mud
- smallest two constituents
- size discrimination
- definition
- encountered when
- what else do samples often contain
- encompasses silt and clay (smallest sediments) with some sand and gravel
- mud particles typically = <0.063 mm
- mud is any sediment that has a sticky character when wet so good form of TE
- clings to stuff – big tick for transfer thinking about background transfer, persistence
- chances of finding in UK is high
- encountered frequently in casework on skin, under fingernails, on clothing/footwear, in/on vehicles; from coastal/river floodplains, fields, and woodlands
- many samples also contain organic matter (grass, weeds, pollen)
define soil
- definition
- homogeneous/heterogeneous
- how is it found on earths crust
- how are they dictated
- what is it made up of
- soil is unconsolidated stable material on the Earth’s surface (it is loose (isn’t a lump) and it is on the surface rather than inside the earth); plant growing material (it is biologically active – good medium)
- extremely heterogeneous so good form of TE as is highly variable
- but need to take care when using microscopic techniques to understand chemical variety in sample (cannot test one area and assume representative of whole sample)
- soil is present on earth’s crust in distinct layers - horizons
- soils are dictated by how they are formed or where they are found:
- climate (arid, hot cold, wet, or dry)
- parent material (what type of rock)
- age (older soil = more fertile and denser, because longer it has had to form)
- biological activity
- topography determine soil type formation
- soil is made up of:
- non-living: inorganic minerals, salt crystals, decaying plant/animal matter (humus), shells, insect exoskeletons, fossils, bones, and teeth
- living: bacteria, algae, fungi, plant roots, invertebrates, small mammals
- unusual: cement, plaster, metallic fragments, glass, paint flakes, paper, fibres, plastic fragments
define dirt and grime
dirt - combination of dust and soil
grime - wet dirt
Why is soil a good form of TE?
- good form of TE as can work out where it is from using UK soil observatory database by British geological survey
- database that lets you search almost any part of UK by any criteria you want
- can put in anything found from analysing trace of soil and will tell where likely find that exact makeup/composition of soil
- unusual components of soil (cement, plaster, metallic fragments, glass, paint flakes, paper, fibres, plastic fragments) are useful in TE too
Define dust (size, size repercussion, chemical compositions)
- particles generally <100 μm
- if <10 μm, can be transported thousands of miles
- this size has big repercussion when trying to determine background, persistence, activity level
- need to bear in mind that size of dust particle may mean it didn’t originate there – might have been carried in wind
- chemical composition varies considerably and is indicative of geographical area or type of place it came from
- natural, industrial (will be different might have soot from chimneys), household (predominantly skin cells), street (particles from brake dust/exhaust fumes), water sources, etc.
define minerals
- definition
- most abundant category
- phyllosilicate class
- also known as
- define clay
- another geological form of TE
- silicate minerals
- phyllosilicate class most interesting
- comprised of sheets of repeating SiO4 tetrahedra - gives minerals from this class a crepe-y appearance and allows them to be fractured easily
- also known as clay minerals
- clay - geological sediment (< 2 um)
Where do we find different types of minerals
- vermiculite
- muscovite (natural mica)
- kaolinite (china clay)
- magnesium silicate (talc)
- bentonite
- hectorite
- Illite (French green clay)
- vermiculite – grey mineral
- bit like diatomaceous earth – it is everywhere
- come in different sizes – have different properties
- found anywhere you want insulating or fire retardant properties
- used as the insulating material in fire-resistant safes, chimneys, brake-linings, floor screed, concrete, fire-proof walls
- highly likely to be encountered as a form of trace especially if someone has tried to break into a safe and burgle it – may end up with traces of vermiculite on clothing, tools, shoes and under fingernails – might think it is just dues
- muscovite (natural mica)
- has repeating tetrahedral sheets – good mineral to use in makeup as soft and shiny
- kaolinite (china clay)
- in clay face masks
- magnesium silicate (talc)
- talcum powder
- bentonite
- face masks and mascara
- hectorite
- face masks and mascara
- Illite (French green clay)
- face masks
- good for angry and red skin – soothing and calming properties
What are gemstones?
Where are these likely to be found?
- another form of minerals
- these are minerals that have been cut and polished to be used in jewellery or as ornaments
- not likely that you are going to find gemstones as a trace material for example in tread of someone’s boots but might find in forensic gemology
