Rocks and Minerals

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• Rocks and Minerals

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• No other planet in the solar system has the
  unique combination of fluids of Earth. Earth has
  a surface that is mostly covered with liquid
  water, water vapor in the atmosphere, and both
  frozen and liquid water on the land.

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• Solid Earth Materials

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• Earths Molten Stage
• During the early formation of the Earth it was
  molten
• During this stage the heavier elements such as
  iron and nickel, sank to the deeper interior of
  the Earth.
• This left a thin layer of lighter materials on
  the surface that is mow called the crust.
• The majority of the Earths mass lies below the
  crust

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• Chemical Analysis
• 8 elements make up 98.6 of the crust
• These 8 elements make up the solid materials of
  the Earths crust and are known as rocks and
  minerals.
• A mineral is solid inorganic material of the
  Earth that has both a known chemical composition
  and a crystalline structure that is unique to
  that mineral
• A rock is a solid aggregate of one or more
  minerals that have been cohesively brought
  together by a rock-forming process.

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• (A)The percentage by weight of the elements that
  make up Earth's crust. (B) The percentage by
  weight of the elements that make up the whole
  Earth.

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• Minerals

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• Introduction
• Minerals
• A mineral is solid inorganic material of the
  Earth that has both a known chemical composition
  and a crystalline structure that is unique to
  that mineral
• Rocks
• A rock is a solid aggregate of one or more
  minerals that have been cohesively brought
  together by a rock-forming process.

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• Crystal Structures
• Can be made up of atoms of one or more kinds of
  elements.
• Crystals are classified according to six major
  groups, with subdivisions of each.

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• A crystal is composed of a structural unit that
  is repeated in three dimensions. This is the
  basic structural unit of a crystal of sodium
  chloride, the mineral halite.

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• The structural unit for a crystal of table salt,
  sodium chloride, is cubic, as you can see in the
  individual grains.

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• These quartz crystals are hexagonal prisms.

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• Crystalline substances are classified into six
  major systems isometric, hexagonal, tetragonal,
  orthorhombic, monoclinic, and triclinic. The six
  systems are based on the arrangement of crystal
  axes, which reflect how the atoms or molecules
  are arranged inside. For example, crystals in the
  orthorhombic system have three axes of different
  lengths intersecting at 90O angles while crystals
  in the hexagonal system have three horizontal
  axes intersecting at 60O and one vertical axis.
  Some common examples in each system are
  illustrated here.

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• (A)The geometric shape of a tetrahedron with four
  equal sides. (B) A silicon and four oxygen atoms
  are arranged in the shape of a tetrahedron with
  the silicon in the center. This is the basic
  building block of all silicate minerals.

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• (A)Isolated silicon-oxygen tetrahedra do not
  share oxygens. This structure occurs in the
  mineral olivine. (B) Single chains of tetrahedra
  are formed by each silicon ion having two oxygens
  all to itself and sharing two with other silicons
  at the same time. This structure occurs in
  augite. (C) Double chains of tetrahedra are
  formed by silicon ions sharing either two or
  three oxygens. This structure occurs in
  hornblende. (D) The sheet structure in which each
  silicon shares three oxygens occurs in the micas,
  resulting in layers that pull off easily because
  of cleavage between the sheets.

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• Silicates and Nonsilicates
• Silicates made of silicon and oxygen and make
  up 92 of Earths crust.
• Ferromagnesian Silicates
• made of iron, magnesium, and silicates
• Form a basic tetrahederal structure.
• Higher density and darker color than other
  silicates due to the presence of iron and
  magnesium
• Nonferromagnesiam Silicates
• silicates that do not contain either iron or
  magnesium.
• Lower density and lighter color than the
  ferromagnesian silicates.

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• Compare the dark colors of the ferromagnesian
  silicates augite (right), hornblende (left), and
  biotite to the light-colored nonferromagnesian
  silicates.

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• Compare the light colors of the nonferromagnesian
  silicates mica (front center), white and pink
  orthoclase (top and center), and quartz, to the
  dark-colored ferromagnesian silicates.

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• Structure of silicates
• Isolated tetrahedrons
• Chain silicates
• Sheet silicates
• Framework silicates

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• Nonsilicates make up 8 of Earths crust
• Carbonates
• Sulfates
• Oxides
• Sulfides
• Halides
• Phosphates
• Hydroxides
• Native elements

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• Physical Properties of Minerals
• Color
• A visual measure.
• Not very useful for identification as color of
  minerals varies considerably.
• Streak
• This is the color of the mineral when it is
  finely powdered.
• Rubbed across a piece of tile, leaving a fine
  powder of the mineral on the tile.
• Hardness
• Resistance of the material to being scratched.
• Measured using the Mohs hardness scale, which
  compares the hardness of the mineral to 10
  reference minerals.

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• (A)Gypsum, with a hardness of 2, is easily
  scratched by a fingernail. (B) Quartz, with a
  hardness of 7, is so hard that even a metal file
  will not scratch it.

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• Crystal form
• Related to the internal geometric arrangement of
  the atoms that make up the crystal structure.
• Cleavage
• the tendency of mineral to break along smooth
  planes.
• Depends upon zones of weakness in the crystal
  structure.
• Fracture
• The broken surface is irregular and not in a flat
  plane.

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• Luster
• Surface sheen
• Metallic like metal
• Pearly like pearl
• Vitreous like glass
• Earthy
• Density ratio of the mass of a mineral to its
  volume.
• Specific gravity ratio of mineral density to
  the density of water
• Depends on
• Kind of atoms which make up the mineral
• How the atoms are arranged in the crystal lattice.

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• Mineral-forming Processes

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• Introduction
• Magma
• Molten rock from which minerals are formed
• Lava
• Magma that is forced to the surface
• Influences on the mineral forming process
• Temperature
• Pressure
• Time
• Availability and concentration of ions that are
  in solution

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• Minerals Formed at High Temperatures
• Bowens Reaction Series
• Arranged with minerals at the top that
  crystallize at higher temperature and minerals at
  the bottom that crystallize out at lower
  temperature.

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• Bowen's reaction series. Minerals at the top of
  the series (olivine, augite, and calcium-rich
  plagioclase) crystallize at higher temperatures,
  leaving the magma enriched in silica. Later, the
  residual magma cools and lighter-colored, less
  dense minerals (orthoclase feldspar, quartz, and
  white mica) crystallize. Thus, granitelike rocks
  can form from a magma that would have produced
  basaltic rocks had it cooled quickly.

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• Minerals Formed at Normal Temperatures
• These form at normal temperatures and pressures
  and in contact with atmospheric gases such as
  oxygen, carbon dioxide, and water.
• There are most of the non-silicates carbonates,
  sulfates, oxides, halides, and sulfides.

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• Altered Minerals
• These minerals undergo changes in chemistry or
  crystal structure as a result of pressure,
  temperature, or chemical solutions
• Similar to minerals that form under high
  temperatures with similar physical properties.

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• Ore Minerals
• Some minerals are left over after the
  crystallizing of magma
• These elements are flushed away in hot water
  solutions as the magma crystallizes.
• Usually crystallize in rock fractures to form
  thin, flat bodies of mineral material called
  veins.
• If these minerals have some economic value they
  are called ore minerals.

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• Rocks

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• Introduction
• Elements are chemically combined to form minerals
• Minerals are physically combined to form rocks.

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• Igneous Rocks
• Form from molten rock material
• Intrusive igneous rock
• Formed when magma cools deep within the Earths
  surface
• Cools very slowly as it is in contact with molten
  rock.
• Produces course-grained igneous rock.
• Extrusive igneous rock
• Magma that cools above the Earths surface.
• Produces fine-grained igneous rocks.
• This rapid cooling does not allow time for
  crystals to form.

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• Igneous rock classification scheme based on
  mineral composition and texture. There are other
  blends of minerals with various textures, many of
  which have specific names.

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• Granite is a coarse-grained igneous rock composed
  mostly of light-colored, light-density,
  nonferromagnesian minerals. The earth's
  continental areas are dominated by granite and by
  rocks with the same mineral composition of
  granite.

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• This is a piece of obsidian, which has the same
  chemical composition as the granite. Obsidian has
  a different texture because it does not have
  crystals and is a volcanic glass. The curved
  fracture surface is common in noncrystalline
  substances such as glass.

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• Sedimentary Rocks
• Form from material from previously existing rock
• Material is provided by weathering of previously
  existing rock
• Sediments
• Weathered rock materials
• Dissolved rock materials
• Clastic sediments
• Another name for weathered rock materials

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• This is a sample of breccia, a coarse-grained
  sedimentary rock with coarse, angular fragments.
  Compare the grain sizes to the centimeter scale.

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• This is a sample of sandstone, a sedimentary rock
  that formed from sand grains in a matrix of very
  fine-grained silt, clay, or other materials. The
  grains in this sample are mostly the feldspar and
  quartz minerals, which probably accumulated near
  the granite from which they were eroded.

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• This is a sample of limestone, a sedimentary rock
  made of calcium carbonate that formed under water
  directly or indirectly from the actions of plants
  and animals. This fine-grained limestone formed
  indirectly from the remains of tiny marine
  organisms.

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• Chemical sediments
• Another name for dissolved rock material.
• The dissolved materials are ions from mineral and
  rocks that have been completely broken down.
• Removed from solution by
• Chemical precipitation from the solution
• Crystallization from evaporating water.
• Biological sediments.

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• Compaction
• As sediments are laid down grain by grain, the
  mass becomes greater.
• The increasing mass of the sediment layer above
  creates pressure on the layers below.
• Eventually this pressure becomes great enough to
  compact the existing layers into a cohesive rock
  layer.
• Cementation
• After, or during, the compaction process, the
  spaces between the sediment particles become
  filled with a chemical deposit.
• This deposit holds the compacted layers into a
  cohesive mass of sedimentary rock.

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• (A)In compaction, the sediment grains are packed
  more tightly together, often by overlying
  sediments, as represented by the bricks. (B) In
  cementation, fluids contain dissolved minerals
  that are precipitated in the space between the
  grains, cementing them together into a rigid,
  solid mass.

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• Metamorphic Rocks
• Rocks changed by heat, pressure, or hot solutions
  due to
• Movement of the Earths crust
• Heat generated by intrusion of hot magma
• Pressure can change rock by flattening,
  deforming, or realigning mineral grains.
• Foliation
• When the pressure on flat crystal flakes tends to
  align the flakes into parallel sheets.
• Gives the rock the property of breaking along the
  planes between the aligned mineral grains in what
  is known as rock cleavage.

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• Increasing metamorphic change occurs with
  increasing temperatures and pressures. If the
  melting point is reached, the change is no longer
  metamorphic, and igneous rocks are formed.

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• This is a sample of marble, a coarse-grained
  metamorphic rock with interlocking calcite
  crystals. The calcite crystals were
  recrystallized from limestone during metamorphism.

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• This banded metamorphic rock is very old at an
  age of 3.8 billion years, it is probably among
  the oldest rocks on the surface of the earth.

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• The Rock Cycle

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• Earth is a dynamic planet with the surface and
  interior in a constant state of flux.
• Internal changes alter the surface by moving the
  Earths plates, building mountains.
• Seas advance and retreat over the continents
  brining in new materials and taking other
  materials away.
• Rocks are continually being changed by Earths
  forces.

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• The Rock Cycle describes the continually changing
  structure of rocks.
• Igneous, sedimentary, or metamorphic rock are
  just temporary stages in the continuing changes
  that all rocks undergo.

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• A schematic diagram of the rock cycle concept,
  which states that geologic processes act
  continuously to produce new rocks from old ones.