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Geology Facts
Earth’s Layers
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The Earth consists
of a solid inner core
(Fe and Ni), a liquid
outer core (Fe and
Ni), a plastic-like
mantle (Si, O, Fe,
Ni), and a thin
rocky crust (Si, O).
The lithosphere is the crust
and upper mantle
Ocean crust (made of basalt) is thinner,
younger, and denser than continental
crust (made of granite).
Convection currents move tectonic plates. Hot material
rises, cools, becomes more dense, and sinks
• Convergent boundaries are colliding plates which cause folded or
thrust faulted mountains, subduction zones, (volcanic and
trenches) and reverse faults (thrust faults)
Divergent boundaries are dividing plates and cause sea-floor
spreading, mid-ocean ridges, rift valleys, and volcanoes.
Normal faults are produced from this movement.
Transform boundaries slide past each other and
strike slip faults and earthquakes are
produced.
Earthquakes can result with any plate
movement
Hot spots are not related to plate
movement
A fault is a break or crack in the Earth’s
crust where movement has occurred
Volcanic activity is associated with
subduction, rifting, or seafloor spreading
An ocean plate will always sink under a continental
plate because it is more dense, creating a trench
Appalachian Mountains are folded
mountains
3 seismic stations are always needed to find the
epicenter of an earthquake
Earthquake Waves
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P waves travel the fastest and reach the
seismic station first. P waves travel
through solids and liquids. P waves slow
down and bend when they hit the liquid
outer core.
S waves do not travel through liquids.
L waves, surface waves cause the most
damage
Most volcanoes and earthquakes occur in
the “Ring of Fire.”
The San Andreas Fault is responsible for
the earthquakes in California
The North American Plate is traveling in a westward course
The Pacific Plate is traveling in a northwestern course
There are 3 kinds of volcanoes, shield,
composite (also known as strata), and cone
Magma is found underground and
lava is above ground
Minerals
• A mineral is found in nature,
inorganic, solid, with a definite
chemical composition and structure.
(crystalline)
Mineral properties depend on
their atomic structure
Ores are useful and profitable
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Ores of Common Metals
Contains: bauxite, bornite, chalcopyrite,
chalcocite, pit ore, magnetite, hematite, specular
hematite, galena, pyrolusite, garnierite,
sphalerite, chromite, stibnite, and molybdenite.
Minerals are determined by their streak, cleavage,
fracture, hardness, color, luster, and special properties
• Streak- The color of the mineral in powder form.
This test is done by rubbing the mineral across a
white streak plate. Several minerals have a streak
that is not the same color as the mineral itself.
Most metallic luster minerals have a dark colored
streak
Cleavage and Fracture
• Cleavage or Fracture- If a mineral breaks along flat, smooth surfaces
it shows cleavage. Cleavage can be in one, two or three directions.
Some examples are:
• Mica- cleavage in one direction, see the diagram below (upper right),
• Feldspar- cleavage in two directions, see the diargam below (lower
left),
• Calcite, Galena and Halite- cleavage in three directions, see the diargam
below (lower right).
• If a mineral breaks along irregular rough surfaces it shows fracture.
Quartz shows a special type of fracture called concoidal (shell-like)
fracture.
Hardness
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Hardness- The ability of one mineral to scratch another. The softer mineral gets
scratched. You test a mineral's hardness by scratching the unknown mineral with an
object of known hardness. Moh's Scale of Hardness is used to rate the hardness of a
mineral. The chart below shows the ten minerals that make up the hardness scale and
some common materials with their hardness to test unknown minerals. One on the scale
is the softest and ten is the hardest.
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To find the hardness of a mineral you first have to find out what it can scratch and what
can scratch it. For example, if a mineral can scratch glass but can't scratch a streak plate,
the mineral has a hardness of 6 on the Moh's Hardness Scale.
Color
• Color- The most
easily observed
property, but usually
the least useful. A
mineral's color can be
changed by the
impurities that are
found in the mineral.
Luster
• Luster- The way light is reflected from a newly exposed
surface. Described as either metallic or nonmetallic. Some
examples of minerals with metallic luster are pyrite, galena
and magnetite. Some examples of minerals with nonmetallic
luster are calcite, quartz and feldspar. Nonmetallic luster can
also be described as glassy, pearly, waxy and earthy (dull).
Special Properties
• Acid test- This test is performed by dropping weak
hydrochloric acid on the mineral. If it reacts (fizzes) then
the mineral is calcite. This test will also help to identify the
rocks limestone and marble, because calcite is the principal
mineral in both.
• Magnet test- If there is a magnetic attraction between your
mineral and a metal object, then the mineral has a high iron
content. The mineral magnetite will attract metal objects.
Igneous Rocks
Igneous rocks are classified by
their composition and texture
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Igneous rocks are produced by the cooling of
magma or lava.
Fast cooling = extrusive, small crystals. Slow
cooling = intrusive, larger crystals
Extrusive small grains, glassy, air holes
present (obsidian, pumice, basalt)
Intrusive large grained, granite
Metamorphic formed by heat and
pressure
Metamorphic classified as foliated
(banded) or non foliated
• Foliated rocks are slate,
schist, gneiss
• Non-foliated include
marble and quartzite
Limestone morphs into marble.
Sandstone morphs into quartzite
Sedimentary
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Sedimentary rocks are formed from rock fragments,
organic material, or chemical precipitation
Sedimentary are classified as clastic, organic, and
chemical
Limestone is formed both chemically
and organically
• Sedimentary are found in flat layers or strata.
Fossils are found in these layers
Clastic rocks are made of fragments –
conglomerate, sandstone, shale
Destructive Geology
• Chemical weathering occurs
mainly in warm, humid climates
Weathering can occur as either a
mechanical or chemical process
Erosion is the process of materials being transported by
moving water, ice, wind, or gravity
Streams and moving water are the
major agents of erosion
Deposition is the dropping or settling
out of sediments
High erosion= high relief areas,
high deposition= low relief areas
Large particles settle out first, sediment size from
largest to smallest- sand, silt, clay
As particle size increases, permeability
increases (ability to hold water).
• Permeability is the ability of a material to drain
Porosity is the amount of pore space
in a rock or sediment
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Different grain sizes and packing arrangements result in different porosity
values. Top: individual pore spaces decrease in size with decreasing grain size.
Bottom: porosity varies with packing (arrangement) of grains.
Soil evolution starts with the weathering of bedrock
Organic material must be present in order to have
soil. (humus)
Soil profiles consist of 3 horizons: O topsoil (humus) most evolved,
A less humus, leaching of minerals from A, and B weathered rock
C These layers are on top of bedrock
Groundwater layers from the surface down would include zone of
aeration, water table, and zone of saturation
An aquifer is a layer of rock that
transports groundwater freely
• A spring is an area where the water table
reaches land’s surface
The watersheds of Virginia are the Sounds of North
Carolina, the Chesapeake Bay, and the Atlantic Ocean.
The Coastal Plain is the flattest area underlain by all the types of
sediments produced by the erosion of the Appalachian Mountains
Piedmont is underlain by igneous and metamorphic rocks produced by
ancient volcanoes. Separated by the fall line from the Coastal Plain.
Blue Ridge Mountains are oldest in the state
they were produced by converging plates.
Valley and Ridge long parallel ridges composed of folded and
faulted rocks that occurred during the collision of Africa
and North America during the Paleozoic.
• Karst Topography and fossils are abundant
Karst topography has caves and sinkholes produced by
acidic groundwater dissolving limestone
Appalachian underlain by sedimentary rocks. Coal
resources are found here. Fossils present.
Virginia resources include limestone, coal
and gravel
Renewable resources can be replaced by nature at a rate at which
they are used. Includes vegetation, water, and soil
Nonrenewable resources are renewed very slowly or
not at all. Includes coal, oil, and minerals
The Earth’s water supply is
renewable but also finite
A fossil is the remains, impressions, or
just the evidence of life preserved in rock
Virginia’s fossils are mostly marine and are from
all eras in history
The Principle of Superposition states that the oldest rocks are
found on the bottom of strata and the youngest are found on top
The Principle of Cross-cutting relationships state that an igneous
intrusion is younger than the layers it cuts across
Fossils, Superposition, and Cross-cutting relationships
are used to determine relative ages
Relative ages are placing events in sequence without
assigning exact numerical ages
Absolute age gives numerical age to an event
Radioactive decay or
half-life is used to
determine the absolute age of rocks
Radioactive isotope
Daughter isotope
Half-life (Myrs) Applications
Carbon 14
Uranium 235
Potassium 40
Uranium 238
Rubidium 87
Nitrogen
Lead
Argon 40
Lead
Strontium
140.0057
207713
1300
2064510
8747,000
Formerly living material less than 30,000 yo
Lunar samples, meteorites, pre-Cambrian rocks
Ocean floor basalts, lava flows, some sediment.
Lunar samples, meteorites, pre-Cambrian rocks
Very old rocks, similar to Uranium
1.Uranium dating is used to find the ages of the oldest rocks.
2.Carbon-14 is used to find the ages of human artifacts.
The Earth is about 4.6 billion years old
Enough is enough………..
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