Rocks:

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Rocks Mineral Mixtures
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• All rocks are heavy.
• True or False

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A heavy piece of rock?
Think again!
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• All rocks are hard.
• True or False

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False

• Chalk
• Pumice
• Talc

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• Rocks never change.
• True or False

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False

• Rocks are changed by processes such as
• Melting
• Pressure
• Heat
• Weathering and Erosion

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Minerals

• A mineral is a naturally formed solid that has a
  repeating three-dimensional structure.
• Minerals are the building blocks that make up
  rocks.

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By asking the four questions you can tell if
something is a mineral.

• 1. Is it nonliving material?
• A mineral is inorganic, meaning it isnt
  made of or by living things.
• 2. Is it formed in nature?
• Crystalline materials made by people arent
  classified as minerals.
• Minerals are not formed by plants or
  animals.
• 3. Is it a solid?
• Minerals cant be gases or liquids.
• 4. Does it have a crystalline structure?
• Minerals are crystals, which have a
  repeating inner structure that
• determines the shape of the crystal.

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If you cannot answer yes to all four questions,
you dont have a mineral.

• A crystal is a solid substance in which the atoms
  are arranged in a repeating pattern in three
  dimensions.
• Each mineral has a crystalline structure that
  depends on the elements that make up the mineral.
  The arrangement of the atoms within the crystal
  creates the crystals shape.

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Types of Minerals

• Minerals are divided into two groups based on
  the elements they are made of
• 1 Minerals that contain the elements silicon and
  oxygen are called silicate minerals.
• 2 The nonsilicate minerals do not contain a
  combination of the elements silicon and oxygen.
  Minerals in this group are made up of other
  elements, such as carbon, oxygen, iron, and
  sulfur.

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Identifying Minerals using 7 physical properties

• 1. Color - Small amounts of impurities can
  change a minerals color
• Luster - the way the surface of a mineral
  reflects light. Minerals have metallic,
• sub- metallic, or nonmetallic luster.
• 3. Streak -the color of a mineral in powdered
  form. When a mineral is rubbed against a hard
  plate, the mark left behind is the streak.

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• 4. Cleavage and Fracture - is the tendency of
  some minerals to break along flat surfaces. The
  way that a mineral breaks is determined by the
  arrangement of its atoms.
• 5.Hardness - a minerals resistance to being
  scratched. Scientists use Mohs hardness scale to
  compare the hardness of minerals.
• 6.Density - is the measure of how much matter
  there is in a given amount of space.

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7. Special properties

• FluorescenceCalcite and fluorite glow under
  ultraviolet light.
• Chemical reactionCalcite will fizz when a drop
  of weak acid is placed on it.
• Optical propertiesA thin, clear piece of calcite
  placed over an image will cause a double image.
• TasteHalite has a salty taste.
• MagnetismMagnetite and pyrrhotite are both
  natural magnets that attract iron.
• RadioactivityMinerals that contain radium or
  uranium can be detected by a Geiger counter.

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Review questions

• How do you determine a minerals streak?

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• By scraping the mineral across a ceramic streak
  plate. The color of the material that rubs off
  the mineral sample is the minerals streak.

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• 2. What is the difference between cleavage and
  fracture?

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• If a mineral has cleavage, it breaks along flat
  surfaces.
• Fracture is the way a mineral breaks along curved
  or irregular surfaces
• See page 397 of text for picture

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Minerals Combine to Form Rock

• Rock is a solid mixture of crystals of one or
  more minerals.
• The main classification of rock depends on how
  the rock formed.
• 1. Igneous rock forms when hot, liquid rock,
  
• (magma) cools and hardens.
• 2. Sedimentary rock forms when pieces of rocks
  
• or minerals are compacted or cemented
• together.
• 3. Metamorphic rock forms when existing rock is
  
• heated and squeezed deep inside the
  Earth.

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Each of the three types of rock is further
classified by composition and texture.

• The composition of a rock is its chemical makeup,
  or the combination of minerals from which the
  rock is made.
• The texture of a rock is determined by the sizes,
  shapes, and positions of the minerals that the
  rock contains.
• Rock with large crystals or mineral grains has a
  coarse-grained texture.
• Fine-grained texture describes rock with very
  small or no visible crystals or mineral grains.

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The Rock Cycle

• The rock cycle is the continual process by which
  new rock is formed from old rock material. Each
  type of rock can be changed into every other type
  of rock.

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Igneous Rock

• Igneous rock forms when hot, liquid rock, or
  magma, cools and hardens.
• The type of igneous rock that forms depends on
• 1. composition of the magma and
• 2. the amount of time it takes the
• magma to cool.

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Igneous rock starts out as magma.

• Magma is created in three ways
• 1. when rock is heated,
• 2. when pressure is released,
• 3. when the composition of the rock changes.

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Melting
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3 ways igneous rock can melt into magma or be
created

• Pressure - The high pressure deep inside the
  Earth forces minerals to stay in the solid state.
  When hot rock rises to shallow depths, the
  pressure is released and the rock can melt.
• Temperature - A rise in temperature can cause the
  minerals in a rock to melt. Different melting
  points cause some of the minerals to melt while
  other minerals remain solid.
• Composition - When fluids such as water combine
  with rock, the composition of the rock changes,
  which lowers the melting point of the rock enough
  for it to melt

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Igneous rocks are formed when magma cools.

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• If the magma comes to the surface of the Earth,
  it is called lava.
• Igneous rocks are formed when some of the melted
  magma rises to a higher level in the mantle of
  the earth.
• The magmas temperature lowers (cools) and begins
  to solidifycreating rock. This usually occurs
  at the edges of tectonic plates.

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• Igneous rocks also form when parts of the Earths
  crust cave in and melt.
• This melted crust returns to the surface, cools
  and solidifies.
• Granite and basalt are common types of igneous
  rocks.

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Igneous rocks are broken down into 2 types

• 1 intrusive (plutonic)
• 2 extrusive (volcanic)

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Intrusive Igneous rocks

• Intrusive rocks solidify within the crust of the
  Earth and form great masses of regular crystals.
  
• They are usually hidden because they are formed
  under the crust.
• Uplift and erosion bring these rocks to the
  Earths surface over time, and they become
  exposed.
• When rocks solidify in cracks through which the
  magma flows, it is called an igneous veinand
  both large and small crystals are formed.

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• A geological process called uplift causes areas
  of the Earths crust to rise to higher
  elevations.
• That means, rocks deep inside the earth can be
  moved to the surface by motions of the Earths
  crust. When a rock reaches the surface of the
  Earth, the processes of weathering and erosion
  begin.

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Extrusive igneous rocks

• Extrusive igneous rocks solidify outside the
  crust, after volcanic eruptions.
• They form with very few crystals.

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Magma can cool at different rates. The longer it
takes for magma or lava to cool, the more time
crystals have to grow. The more time crystals
have to grow, that coarser the texture of the
igneous rock.
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Sedimentary rocks are formed when layers of
earth have been deposited in the bottoms of
bodies of water. Over time these layers are
pressed together forming sedimentary rocks.
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• Erosion by wind and water on the Earths surface
  break down rocks into small pieces called
  sediments. These sediments contain organic
  (carbon based lifeform) remains, and are moved by
  the wind and water.

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• In the areas where the fragments are deposited,
  the sediments cling together, become compacted,
  and undergo a CHEMICAL CHANGE!
• This compaction and chemical change is caused by
  great pressure, which cements the fragments
  together and forms sedimentary rock.

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• Limestone and shale are the most common types of
  sedimentary rocks.
• Sedimentary rocks make up 75 of the rocks on the
  Earths land surfaces.
• Sedimentary rocks are classified by their grain
  size.

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Metamorphic rocks were once sedimentary or
igneous rocks that have been placed under tons of
pressure and heat.

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Metamorphic rocks

• Metamorphic rocks have an extremely varied
  composition. They are formed by the
  transformation of igneous or sedimentary rock.
• This change occurs when either igneous or
  sedimentary rock masses are subjected to
  conditions of high pressure and/or temperature.

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This causes the rocks structure to CHANGE
CHEMICALLY and creates new minerals.
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Textures of metamorphic rock

• All metamorphic rock has one of 2 textures
  foliated or non-foliated
• Foliation - Metamorphic rock that is foliated
  contains minerals that are arranged in planes or
  bands. Rocks that contain a variety of minerals
  tend to form foliated rocks.
• Because minerals are aligned, foliated rocks
  split into layers. Metamorphic rocks are often
  classified by their texture (fine, medium or
  coarse-grained).

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Textures of metamorphic rock
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Revisit the Rock Cycle

• Over time, all rock is broken down by the forces
  of wind and water into sediments. This action is
  called weathering.

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Weathering

• Weathering and erosion are the cause of the
  production and movement of sediments.
• There are 2 types of weathering
• Mechanical breaks the rocks apart physically
  without changing the chemical composition of the
  original rock. (Ex. Ice breaks a rock)
• Chemical changes the chemical composition of
  the rock (ex. Acid rain eroding rock).

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• Rocks are continuously changing from one type to
  another, although very slowly, and this process
  is called the rock cycle.

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• As you can see, all the different kinds of rocks
  are being continuously recycled. No matter how
  they are formed, eventually they will be broken
  down by erosive forces.

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• Much of the sediments formed by the wind and
  water erosion are deposited into the sea, where
  new sedimentary rocks will be formed.
• The grinding movement of the Earths tectonic
  plates also recycles rocks. Pieces of igneous
  and seabed sedimentary rock get broken off and
  are added to the cycle.
• These fragments can be dragged downward, where
  new metamorphic rocks can be formed by heat and
  pressure.
• Then volcanoes can bring them back up to the
  surface to form igneous rock? and eventually
  start the erosion process all over again.
• This cycle has been going on for millions of
  years.

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A rock can be a thing of beauty.