Geology Facts

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Geology Facts

                                                                                        U.S. Department of the InteriorU.S. Geological SurveyContact Kate BartonLast Modification 18 Oct 2000 (ebj)USGS Privacy Policy

                                                                                        U.

                                                                                                                 
For more information, please visitVirginia Division of Mineral Resources

                                                                                                                 
For more information, please visitVirginia Division of Mineral Resources
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Earths Layers

• 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).

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The lithosphere is the crust and upper mantle
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Ocean crust (made of basalt) is thinner, younger,
and denser than continental crust (made of
granite).
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Convection currents move tectonic plates. Hot
material rises, cools, becomes more dense, and
sinks
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• Convergent boundaries are colliding plates which
  cause folded or thrust faulted mountains,
  subduction zones, (volcanic and trenches) and
  reverse faults (thrust faults)

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Reverse Fault
Normal Fault
transform, lateral, slip-strike fault
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Divergent boundaries are dividing plates and
cause sea-floor spreading, mid-ocean ridges, rift
valleys, and volcanoes. Normal faults are
produced from this movement.
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Transform boundaries slide past each other and
strike slip faults and earthquakes are produced.
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Earthquakes can result with any plate movement
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Hot spots are not related to plate movement
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A fault is a break or crack in the Earths crust
where movement has occurred
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Volcanic activity is associated with subduction,
rifting, or seafloor spreading
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An ocean plate will always sink under a
continental plate because it is more dense,
creating a trench
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Appalachian Mountains are folded mountains
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3 seismic stations are always needed to find the
epicenter of an earthquake
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Earthquake Waves

• 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

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Most volcanoes and earthquakes occur in the Ring
of Fire.
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The San Andreas Fault is responsible for the
earthquakes in California
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The North American Plate is traveling in a
westward courseThe Pacific Plate is traveling in
a northwestern course
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There are 3 kinds of volcanoes, shield, composite
(also known as strata), and cone
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Magma is found underground and lava is above
ground
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Minerals

• A mineral is found in nature, inorganic, solid,
  with a definite chemical composition and
  structure. (crystalline)

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Mineral properties depend on their atomic
structure
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Ores are useful and profitable

• Ores of Common Metals
• Contains bauxite, bornite, chalcopyrite,
  chalcocite, pit ore, magnetite, hematite,
  specular hematite, galena, pyrolusite,
  garnierite, sphalerite, chromite, stibnite, and
  molybdenite.

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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

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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.

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Hardness

• 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.
• 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.

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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.

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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).

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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.

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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

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Extrusive small grains, glassy, air holes present
(obsidian, pumice, basalt)
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Intrusive large grained, granite
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Metamorphic formed by heat and pressure
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Metamorphic classified as foliated (banded) or
non foliated

• Foliated rocks are slate,
• schist, gneiss
• Non-foliated include
• marble and quartzite

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Limestone morphs into marble. Sandstone morphs
into quartzite
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Sedimentary

• Sedimentary rocks are formed from rock fragments,
  organic material, or chemical precipitation
• Sedimentary are classified as clastic, organic,
  and chemical

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Limestone is formed both chemically and
organically

• Sedimentary are found in flat layers or strata.
  Fossils are found in these layers

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Clastic rocks are made of fragments
conglomerate, sandstone, shale
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Destructive Geology

• Chemical weathering occurs mainly in warm, humid
  climates

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Weathering can occur as either a mechanical or
chemical process
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Erosion is the process of materials being
transported by moving water, ice, wind, or
gravity
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Streams and moving water are the major agents of
erosion
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Deposition is the dropping or settling out of
sediments
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High erosion high relief areas, high
deposition low relief areas
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Large particles settle out first, sediment size
from largest to smallest- sand, silt, clay
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As particle size increases, permeability
increases (ability to hold water).

• Permeability is the ability of a material to
  drain

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Porosity is the amount of pore space in a rock or
sediment

• 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.

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Soil evolution starts with the weathering of
bedrock Organic material must be present in
order to have soil. (humus)
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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
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Groundwater layers from the surface down would
include zone of aeration, water table, and zone
of saturation
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An aquifer is a layer of rock that transports
groundwater freely

• A spring is an area where the water table reaches
  lands surface

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The watersheds of Virginia are the Sounds of
North Carolina, the Chesapeake Bay, and the
Atlantic Ocean.
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The Coastal Plain is the flattest area underlain
by all the types of sediments produced by the
erosion of the Appalachian Mountains
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Piedmont is underlain by igneous and metamorphic
rocks produced by ancient volcanoes. Separated
by the fall line from the Coastal Plain.
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Blue Ridge Mountains are oldest in the state they
were produced by converging plates.
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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

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Karst topography has caves and sinkholes produced
by acidic groundwater dissolving limestone
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Appalachian underlain by sedimentary rocks. Coal
resources are found here. Fossils present.
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Virginia resources include limestone, coal and
gravel
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Renewable resources can be replaced by nature at
a rate at which they are used. Includes
vegetation, water, and soil
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Nonrenewable resources are renewed very slowly or
not at all. Includes coal, oil, and minerals
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The Earths water supply is renewable but also
finite
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A fossil is the remains, impressions, or just the
evidence of life preserved in rock
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Virginias fossils are mostly marine and are from
all eras in history
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The Principle of Superposition states that the
oldest rocks are found on the bottom of strata
and the youngest are found on top
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The Principle of Cross-cutting relationships
state that an igneous intrusion is younger than
the layers it cuts across
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Fossils, Superposition, and Cross-cutting
relationships are used to determine relative ages
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Relative ages are placing events in sequence
without assigning exact numerical ages
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Absolute age gives numerical age to an event
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Radioactive decay or half-life
is used to determine the absolute age of rocks

• Radioactive isotope Daughter isotope
  Half-life (Myrs) Applications
• Carbon 14 Nitrogen
  140.0057 Formerly
  living material less than 30,000 yo
• Uranium 235 Lead
  207713 Lunar
  samples, meteorites, pre-Cambrian rocks
• Potassium 40 Argon 40
  1300 Ocean
  floor basalts, lava flows, some sediment.
• Uranium 238 Lead
  2064510 Lunar
  samples, meteorites, pre-Cambrian rocks
• Rubidium 87 Strontium
  8747,000 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.

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The Earth is about 4.6 billion years old
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Enough is enough..

• Remember
• Make sure you understand the question
• Read all the answers
• Slash the trash, get rid of the ones you know are
  not the answer
• When you are left with 2 answers, use the one
  that was your first choice