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Transcript of Geology Facts U.S.Departmentofthe InteriorU.S.GeologicalSurveyContact:Kate BartonLastModification:18...
Geology Facts
U.S. Department of the InteriorU.S. Geological Survey
Contact: Kate Barton
Last Modification: 18 Oct 2000 (ebj)USGS Privacy Policy
U.
Earth’s 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).
Ocean crust (made of basalt) is thinner, younger, and denser than continental crust (made of granite).
• 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.
An ocean plate will always sink under a continental
plate because it is more dense, creating a trench
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
The North American Plate is traveling in a westward course
The Pacific Plate is traveling in a northwestern course
Minerals
• A mineral is found in nature, inorganic, solid, with a definite chemical composition and structure. (crystalline)
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.
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• 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.
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 are produced by the cooling of magma or lava.
• Fast cooling = extrusive, small crystals. Slow cooling = intrusive, larger crystals
Metamorphic classified as foliated (banded) or non foliated
• Foliated rocks are slate,
schist, gneiss
• Non-foliated include
marble and quartzite
Sedimentary
• 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
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
• 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.
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
Renewable resources can be replaced by nature at a rate at which
they are used. Includes vegetation, water, and soil
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
Radioactive decay or half-life is used to
determine the absolute age of rocks Radioactive isotope Daughter isotope Half-life (Myrs) ApplicationsCarbon 14 Nitrogen 140.0057 Formerly living material less than 30,000 yoUranium 235 Lead 207713 Lunar samples, meteorites, pre-Cambrian rocksPotassium 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.