Download Structure of Earth and Minerals

Shape of Earth
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Gravity
–  Earth is nearly spherical
Spin
–  Earth bulges at equator
Distribution of continents
–  Slightly pear shaped
Topographic relief
–  Minor compared to planet’s size
Location Systems
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Latitude and longitude
–  Latitudes (or parallels) are parallel to the equator
Location Systems
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Latitude and longitude
–  Longitudes (or meridians) are formed at right angles to the latitude
lines
•  Prime meridian and international date line
Location Systems
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Prime Meridian and Dateline
–  Prime Meridian
+ runs through Greenwich near London, UK
+ arbitrary
–  Dateline
+ follows 1800
Location Systems
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Tropics of Cancer and Capricorn
–  Tropics of Cancer
+ 23.50N
+ the sun is directly overhead at noon on June solstice
–  Tropics of Capricorn
+ 23.50S
+ the sun is directly overhead at noon on December solstice
Location Systems
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Arctic and Antarctic Circle
–  Arctic Circle
+ 66.50N, it is 23.50 south of the North Pole
+ on the March equinox, the Sun rises and does not set for 24 hours
–  Antarctic Circle
+ 66.50S, it is 23.50 north of the South Pole
+ on the March equinox, the Sun set and does not rise for 24 hours
Location Systems
Charts and maps
–  Distorted images of
Earth’s curved surface
–  Projection types: cylindric,
conic, and tangent
Tangent projection
Greenland
–  Size and shape are close to its true form on Earth
Conic projection
Greenland
–  Island has grown larger
Cylindric projection
Greenland
–  Size and shape are greatly distorted
Location System
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Measuring latitude
–  North Star, Polaris
–  Southern Cross
Location System
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Longitude and time
–  Use of clocks to record the time the Sun is at its zenith
–  Greenwich Mean Time (GMT) or Universal Time
Location System
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Longitude and time
–  Use of clocks to record the time the Sun is at its zenith
–  Greenwich Mean Time (GMT) or Universal Time
The Water Planet
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Reservoirs and residence time
–  Large reservoirs ! long residence time
–  Small reservoirs ! short residence time
Structure of the Earth
Origin of our System of Planets
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“Big Bang”
•  Most widely accepted scientific explanation
•  ~12-13.5 Billion years ago
•  This eventually led to…
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The Nebular Hypothesis
The Nebular hypothesis
Formation of the Sun
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Proto-Sun
•  Matter pulled into centre of disk by gravity
Sun
•  High density heats it up starting spontaneous fusion
•  Emits energy in the form of light & heat
Formation of the Planets
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Terrestrial
•  Denser material (dust) accumulated in inner regions
•  Planetesimals formed from accreted material
–  These eventually collided to form Terrestrial
planets and moons
Gas giants
•  Less dense matter (gas) accumulated in outer regions
Differentiation
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The surface was heated due to meteor impacts
Caused the Earth to partially melt & density stratification.
–  Gravity pulled most of the iron to the core
–  Lighter minerals rose towards the surface
Formation of the Earth
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First surface on the Earth formed ~4.6 billion years ago.
A collision with a rocky body about the size of Mars smashed into the Earth
–  Rocky mantle of the object formed a debris ring around the Earth
–  The metallic core merged with the Earth’s
–  May have formed the Moon
Energy
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Forms of Energy
–  Gravitational, Heat, Chemical, Radiant, Nuclear and Elastic (strain)
Energy
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Sources of Energy
–  External
•  Solar energy – 99.987% of total energy reaching surface
–  Internal – 0.013% of total energy
•  Radioactive Decay – 235U, 232U, 232Th, 40K
–  not much around, but enough!
•  Conversion of Gravitational Energy
Origin of the Oceans
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Water from interior of Earth
–  Mantle
–  Gas that escape volcanoes is 70% water vapor
–  4 billion years at current rate ! 100 times the volume
of the oceans
Water from outer space
–  10 million comets enter the atmosphere each year
–  Layer of water 0.0025 mm deep added each year
–  4 billion years at current rate ! 2 to 3 times the
volume of the oceans
Age and Time
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Age of Earth
–  History of estimates
•  Bible, cooling time, rate of addition of salt in oceans by rivers,
radiometric dating
–  Radiometric dating ! 4.5-4.6 billion years
Geologic time
–  Eons, eras, periods, epochs
–  Important events
Radiometric (Absolute) Age
Determine the actual number of years that have passed since an event occurred
using radioactive decay
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Radioactivity - 1896
Parent – an unstable
radioactive isotope
Daughter product –isotopes
resulting from decay of a
parent
Half-life –time required for
one-half of radioactive nuclei
in a sample to decay
Age of the Earth?
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Oldest rock? 4.28 Billion Yrs
–  Real age? NO
–  BUT can use Meteorites
•  (non-differentiated rocks) ~4.6 Billion yrs
–  Apollo Moon samples ~4.0-4.6 Billion yrs
Deciphering the Earth’s Structure
  How do we know the earth is layered?
–  Earth’s Mass
–  Seismic Rays
•  P and S
waves
–  Field Observations
•  Rocks and
Meteorites
Deciphering the Earth’s Structure
P-waves
  How do we know the earth is layered?
–  Arrival times of seismic waves
•  Generated by earthquakes, volcanic eruption,
human-made explosions
•  Speed depends on chemistry, density and
physical state (solid, partially molten, molten)
•  Types of waves
S-waves
Deciphering the Earth’s Structure
  How do we know the earth is layered?
–  Arrival times of seismic waves
•  Shadow zones
The Earth’s Layering
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Internal layers
–  Inner core
–  Outer core
–  Mantle
–  Crust
–  Mohorovičić
discontinuity, or Moho
The Earth’s Layering
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Internal layers can be defined
by
–  Chemical composition
–  Physical properties
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Layers defined by
composition
–  Crust (0-40 km)
–  Mantle (40-2900 km)
–  Core
Outer Core
(2900-5200 km)
Inner Core
(5200-6400 km)
The Earth’s Layering
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4 main layers
–  based on physical
properties &
mechanical strength
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Lithosphere
Asthenosphere
Mesosphere
Core
The Earth’s Layering
Isostasy
Buoyant support
of lithosphere by
asthenosphere
Oceanic Crust
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makes up 65% of total crust
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Uniform thickness:
3 to 10 km, average 5-7 km
(vs. 35-50 km for
continental)
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Predominantly igneous rock
–  Average composition is
basaltic (s.g. 2.7)
Continental Crust
35% of Earth's surface
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Compared to oceanic crust...
→  thicker (~35-50 km ave but > 70 km
below some mountain belts)
→  less dense (S.G. about 2.5)
→  more silica rich (ave. granite
composition)
→  more complex structure and history
– considerable variability in rock
types and ages
Minerals: Building blocks of rocks
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Definition of a mineral:
•  Naturally occurring
•  Inorganic solid
•  Ordered internal molecular structure
•  Definite chemical composition
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Definition of a rock:
•  A solid aggregate or mass of
minerals. (The mineral grains are
cemented or interlocked together.)
Classification of Minerals
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Nearly 4000 minerals have been identified on Earth
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Rock-forming minerals
–  20-30 Common minerals that make up most of the rocks of Earth’s
crust
–  Only a few dozen members
•  Composed mainly of the 8 elements that make up over 98% of the
continental crust
–  The 2 most abundant elements:
•  Silicon (Si)
•  Oxygen (O)
Classification of Minerals
% elements by WEIGHT
% elements by VOLUME
Average composition of the continental crust
Minerals - Silicates
Olivine
Pyroxene (Augite)
Amphibole (Hornblende)
Biotite
Quartz
Feldspar
Minerals - Silicates - Olivine
Olivine
Olive-green to yellow green; vitreous to
dull luster; H = 6.5 to 7 but often difficult to
test because many samples are granular
aggregates.
Minerals - Silicates - Garnet
Most commonly reddish brown or yellowish
tan; vitreous to resinous luster; H = 6.5 to
7.5; D = 3.6 to 4.3; twelve-sided crystals
(diamond-shaped faces) or roughly
spherical crystals common. Broken surfaces
may resemble cleavage in some large (> 1
cm) samples.
Minerals - Silicates - Pyroxene
Augite
Black to dark green; H = 5 to 6; D = 3.2 to
3.4; vitreous to dull luster; two imperfect
cleavages meet at nearly 90°; a pyroxene
mineral. Another pyroxene, diopside, is
similar but is light grayish green.
Minerals - Silicates - Amphibole
Hornblende
Black; H = 5 to 6; D = 3.0 to 3.4; vitreous
luster; may have faint green-gray streak;
two perfect cleavages meet at 124° and
56°, but cleavage faces are commonly
stepped rather than smooth; splintery
appearance.
Minerals - Silicates - Mica
Biotite
Muscovite
Biotite: Brown to brownish black; vitreous
luster; H = 2.5 to 3.0; D = 2.8 to 3.2; may give
a brown-gray streak; individual crystals are
commonly small and cleavage surfaces are
wavy; one perfect cleavage; transparent,
flexible and elastic in thin sheets.
Muscovite: Colorless, silvery white,
brownish; vitreous luster; H = 2.0 to 2.5; D =
2.8 to 2.9; one perfect cleavage; transparent,
flexible, and elastic in thin sheets.
Minerals - Silicates - Feldspar
Orthoclase
Plagioclase
Orthoclase: Salmon-pink, white, gray, green;
vitreous luster; H = 6; D = 2.5 to 2.6; two
cleavages meet at nearly 90°; no striations.
Plagioclase: White to dark gray; sometimes
buff; vitreous luster; H = 6; D = 2.6 to 2.8; two
cleavages meet at nearly 90°; some cleavage
faces have very fine, perfectly straight parallel
striations, which show up in reflected light.
Minerals - Silicates - Quartz
Coarsely crystalline varieties: clear, milky,
white, purple, smokey gray; pink;
transparent to translucent; vitreous luster; H
= 7; D = 2.7; conchoidal fracture; usually
massive but six-sided crystals popular in
rock shops; Microcrystalline varieties:
chert(gray, dull luster), flint (black, dull
luster), chalcedony (brown to gray,
translucent, waxy luster), agate and onyx
(varicolored bands, vitreous luster).
Minerals - Non-Silicates
Oxides
Sulfides
Sulfates
Hematite
Pyrite
Carbonates
Elements
Gypsum
Calcite, dolomite
Diamonds
Minerals - Non-Silicates - Oxides
Hematite
First variety: steel gray to dull red; H =
6; D = 5.0; red-brown streak; may be
micaceous (tiny flakes) or massive.
Second variety: Red to reddish brown,
H = 1.5 to 5.5; D = 5.0; dull luster; redbrown streak; earthy or oolitic (made of
spherical structures 0.25 to 2 mm in
diameter) masses.
Minerals - Non-Silicates - Sulfides
Pyrite
Brass-yellow; H = 6 to
6.5; D = 5.0; greenish
black to black streak;
massive or as
crystals (cubes or
pyritohedra).
Galena
Lead grey, silvery; H =
2.5 to 2.75; D = 7.4-7.6;
metallic lustre; lead grey
streak; tabular, massive
or as crystals (cubes or
octahedra); cubic
cleavage
Minerals - Non-Silicates - Sulfates
Gypsum
Clear, white, light gray; HSulfates
= 2; D =
2.3; vitreous to pearly luster; may be
able to flake off small brittle sheets;
one perfect cleavage and two poor
cleavages indicate the selenite
variety of gypsum; alabaster is
massive, satin spar is fibrous.
Minerals - Non-Silicates - Carbonates
Calcite
Calcite: Clear, white, other colors
less common; vitreous luster; H =
3; D = 2.7; three perfect
cleavages form rhombohedric
cleavage fragments; double
image seen through clear pieces;
reacts strongly with dilute
hydrochloric acid.
Dolomite
Dolomite: Buff, gray, white,
pinkish; H = 3.5 to 4; D = 2.8 to
2.9; small, rhombohedral crystals
or massive; three cleavages not
at 90°, may be indistinct; unless
powdered, reacts slowly or not at
all with dilute hydrochlorite acid.
Minerals - Non-Silicates - Elements
Diamonds (Carbon): colourless to
black; H = 10; D = 3.5; white streak;
perfect cleavage in four direction;
Diamonds
Graphite (Carbon): steel black to gray;
H = 1-2; D = 2.1-2.2; black streak;
perfect cleavage in one direction;
tabular, six-sided foliated masses;
metallic lustre;
Sulfur
Graphite
Sulfur: range of yellows; H = 2; D =
1.9-2.1; yellow streak; can have vitreous
lustre, but more often resinous or earthy
Minerals - Summary
•  Silicate minerals vs. non-silicate minerals
•  Silicate minerals are by far the most abundant in the crust
(ca. 92 %)
•  Feldspar and Quartz the most common silicate minerals
•  Non-silicate minerals: carbonates, elements, oxides,
sulfates, and sulfides
Mineral resources
Ore Deposits
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Ore – rock in which a valuable or useful metal occurs to be economic to mine
Concentration Factor (CF): CF = Cm/Cmc
–  Cm = Concentration factor of the metal in the ore
–  Cmc = Concentration of the metal in average continental crust
The higher the CF - the richer the ore
Examples of metals obtained from ores
–  Aluminum or Iron – appliances and vehicles
–  Metals for conductors or semi-conductors
–  Gems, gold, and silver – jewelry
–  Lead from galena
–  Copper from malachite and azurite
–  Zinc from sphalerite
–  Many other metals found in rocks
Cost Factors & Distribution
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Concentration Factor (CF)
4 to 25,000 times CF
–  highly variable occurrences
World demand and many market factors
Energy cost
Human/labor cost
Distance to processing or market
Environmental cost - remediation
Globally, very un-even distribution
–  Some countries have plenty – export nations
–  Some countries have none – import nations
Un-even distribution is reason wars are fought
World Mineral Supply
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World demand is
always fluctuating
Commodities do not
follow fluctuating
trends
Mineral reserves
eventual will be
depleted
Import/export
relationships will
fluctuate
Technology often
allows more access to
difficult or low grade
ore deposits
Future mineralresource shortages will
occur and cause
international tension
Surface Mines
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Quarrying extracts rock to be used either intact (building blocks or facing
stone) or crushed (cement-making and road bed)
Open-pit
–  Mine a large ore body located near the surface
–  Permanent changes to local topography will occur
Strip mining
–  Most ores occur in a layer that generally is parallel to the surface
–  The ore zone is overlain by vegetation, soil, non-ore rock that must be
removed
–  Spoils banks are designed to collect the waste rock
–  Current reclamation law requires that it be returned to the pit and the
original soil replaced
–  Expensive but vital
Seabed Resources
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Sand and gravel
–  calcium oxide, calcium carbonate (currently mined)
–  Dissolved chemical products (Ca, Mg, Si, Na, K, Cl, etc. are transported
by surface flow and groundwater to ocean basins
–  When concentration sufficiently high, these precipitate by chemical
means or by organisms (to build their skeletons)
–  Subtropical and tropical areas with major reefs which are also source for
limestone used in cement and other industrial uses
gypsum
Seabed Resources
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Evaporites (halites, gypsum)
–  Form on arid marine coastlines (Sabkhas) or where marine basins
become restricted and get
oversaturated in salts
Seabed Resources
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Oil and gas (currently extracted)
Geochemical hazards
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Exposure to naturally occurring chemicals, either directly or through our food
or water, that are detrimental to human health.
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Divide elements into 3 groups:
–  Essential Macronutrients – C, H, O, N, Ca,
P, S, K, Na, Cl, Mg
(required in large amounts >100 mg/day)
–  Essential Micronutrients – Cr, Co, Cu, F, I,
Fe, Mn, Mo, Se, Zn, Ni, Si, Sn, V (only a few
mg needed/day – can be harmful in excess)
–  Toxic Elements – Al, As, Cd, Pb, Hg, Rn
(not required & harmful in excess)
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Effects of geochemical hazards often slow and
cumulative,
–  human activities often increase risks.
Arsenic (As) in Bangladesh
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Aquifer is the sole drinking water source for
110 million people from Bangladesh & India
As associated with aquifers occurring at
intermediate depth wells (very shallow &
deep (>150 m) wells unaffected
Organic C-rich sediments in aquifers
–  release of As into groundwater
Concentrations of As in drinking & irrigation
water as high as 4000 ppb
–  WHO drinking water standard: 10 ppb
–  Bangladesh Gov. limit: 50 ppb
25-75 Million people affected by Arsenic
poisoning
Arsenic (As) in Bangladesh
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Effects of poisoning take 5-15 years to become apparent
As poisoning characterized by sores on the chest / blackened palms
Different cancers have been linked to arsenic in the drinking water
People did not realize that As was present in the drinking water since it is
colorless, tasteless & odorless
6 to 10 million wells
Radon gas
•  Produced during decay
of 238U
•  Rn gas has very short
half-life - 3.6 days
–  usually no problem
outside or if good
ventilation
•  Amount of Rn gas in
homes is dependant on
–  Concentration of U
in rocks
–  Fracturing of rocks
in the ground
–  Nature & condition
of overlying soil
–  Building design
Asbestos
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Widely used in construction, insulation,
and manufacturing
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an industrial term derived from mining and
manufacturing material of asbestiform
habit
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Occurs throughout much of the planet
–  In 2/3 of the rocks in the earth's crust
–  Fibres released by erosion & carried
by the wind
–  You are most likely inhaling between
10,000 and 15,000 fibres/day!!
Mineralogy of Asbestos
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Amphibole asbestos (“blue asbestos”)
–  Tremolite, Anthophyllite, Actinollite,
Crocidolite, Amosite
–  Resists acid & extremely high T
–  Used in industrial furnaces & heating systems.
–  Fibres stay much longer in the lungs than
Serpentine fibres so more likely to inflict
damage and cause disease
–  been drastically controlled & largely replaced.
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Serpentine asbestos (“white asbestos”)
–  Chrysotile
–  Found in almost all asbestos-based products
available today & main form (>90%) still mined
–  Different from amphiboles both structurally &
chemically.
–  basically harmless
Asbestos through history
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Used for >2,000 years. Named by the
Ancient Greeks, meaning
"inextinguishable".
Fireproof cloth
–  fibers woven like cotton
–  Greeks used it as funeral dress for the
cremation of kings
–  Rumoured that Romans cleaned
asbestos napkins by throwing them in
fire. Cloth would come out of fire whiter
than it went in
–  1800s & 1900s asbestos stage curtains
•  limelights
Hazards noted
–  Pliny the Younger (A.D. 61-114)
mentions “sickness of the lungs” in
slave asbestos weavers
Health risks of Asbestos
Health risks only when fibres are present in the air that people breathe.
Normally 200,000-2 million fibres/l in drinking water
In parts of Québec – 170 million fibres/l – BUT…
Exposure depends on:
Concentration of asbestos fibres in the air
Duration of exposure
Frequency of exposure
Size of the asbestos fibres inhaled
Amount of time since the initial exposure.
When inhaled in significant quantities, fibres can cause:
asbestosis (scarring of the lungs -> makes breathing difficult)
mesothelioma (rare cancer of lining of the chest or abdominal cavity)
Latent period of ≥ 20 years
lung cancer
Smoking + inhaled asbestos, greatly increases risk of lung cancer
Risk of the asbestos worker who smokes is 90 times greater than the non-asbestos, nonsmoking worker
Thetford Mines, Quebec - 1970s
•  Discovered lab. connection between
cancer in rats & exposure to large
quantities of asbestos
•  Looked for correlation between
human exposure and cancer.
•  Thetford Mines is built around a mine
& mill devoted to the production of
chrysotile asbestos.
•  Study looked at mortality rate of male
workers since mine opened
•  Unusually high % of cancer-caused
deaths occurred in TM relative to the
rest of Canada.
•  BUT study was scientifically flawed
•  Failed to report/consider that nearly
all (85-90%) of the workers also were
heavy smokers!!
•  Media & more radical
environmentalists used this flawed
study to promote ban on all asbestos.
Asbestos risk
Safe Asbestos?
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Asbestos Cement Products (panels, facings,
extruded products, pipes and fittings, ducts, sheets,
shingles)
Paper Boards (thermal insulators, electric insulators)
Friction Materials (brake linings, clutch facings,
industrial friction materials)
Coatings (sprayed plastic, premixed underbody)
Protective Metal Sheets
Texturized Paint
Textiles (yarn, packing, fabric, belts, sealing flanges,
casing, protective clothing)
Felts (bitumen saturated pipe line & roofing)
Paper (inorganic bonded & coated cooling tower
papers, resin saturated electrical papers, resin
bonded laminated papers)
Tiles (asphalt tile, vinyl tile, tile adhesives)