Emeralds are a form of the mineral beryl. These gems form deep beneath Earth

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• Emeralds are a form of the mineral beryl. These
  gems form deep beneath Earths surface and are
  found in relatively few locations.

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Minerals and Rocks
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Minerals and Rocks

• A rock is a solid combination of minerals or
  mineral materials.
• Minerals are inorganic, meaning that living
  things did not produce them and they occur
  naturally.
• Geologists dont classify coal as a mineral
  because coal was created from plant remains.
• Materials like brick and concrete are not
  considered minerals either.

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Minerals and Rocks

• Each mineral is a unique substance with its own
  chemical composition and crystal structure.
• For most minerals, the proportion of elements can
  vary slightly while the mineral still retains a
  similar set of characteristics.
• Within each mineral crystal, the chemical
  composition is nearly constant.

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Minerals and Rocks

• Minerals are the building blocks of rocks.
• Only a fraction of the nearly 4000 known minerals
  are common. These common minerals are called the
  rock-forming minerals.
• Each particle within a rock is a separate mineral
  crystal.
• A crystal is a solid in which atoms are arranged
  in a regular repeating pattern.

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Minerals and Rocks

• This portrait of Abraham Lincoln on Mt. Rushmore
  in South Dakota was sculpted in a granite cliff.

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Minerals and Rocks

• Granite is made up of quartz, feldspar, mica, and
  hornblende.
• A magnified view reveals the individual crystals
  of the minerals that make up granite.

Feldspar
Mica
Quartz
Hornblende
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The Properties of Minerals
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The Properties of Minerals

• Crystal Structure
• In each type of mineral, the atoms are arranged
  in a particular geometric shape, or crystal
  structure.
• Each mineral always has the same crystal
  structure.
• The size of a minerals crystals can vary.

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The Properties of Minerals

• Many crystals form long prisms with a specific
  number of sides. Other minerals have crystals
  shaped like cubes, sheets, needles, or threads.
• Halite, the mineral form of table salt, forms
  cubic crystals. Garnet, a red, semiprecious gem,
  often forms 12-sided crystals.

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The Properties of Minerals

• Quartz that is pure silicon dioxide is clear or
  white. Slight impurities produce a range of
  colors, including the violet quartz (amethyst)
  specimen shown here.

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The Properties of Minerals

• Color
• Some minerals can be identified by a
  characteristic color.
• Pyrite, also known as fools gold, is always
  golden in color.
• Crystals of pure sulfur are always yellow.
• But a minerals color can often be deceptive,
  because slight changes in composition can cause
  significant changes in a minerals color.

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The Properties of Minerals

• Streak
• The color of a minerals powder is known as its
  streak.
• A minerals streak can be found by scraping the
  mineral on a piece of unglazed porcelain called a
  streak plate.
• The color of a minerals streak is not always the
  same as the color of the mineral itself.

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The Properties of Minerals

• Although this piece of hematite is silver-gray,
  it can be identified by its red-brown streak.

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The Properties of Minerals

• Luster
• Luster is the way in which a minerals surface
  reflects light.
• A rough, crumbly surface is said to be an earthy
  luster. Other terms that describe luster include
  silky, pearly, and vitreous (glassy.)
• Galena and pyrite have a metallic luster.
• Sulfur has a resinous-to-greasy luster.

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The Properties of Minerals

• Density
• The density of a mineral depends on its chemical
  composition.
• In general, minerals made up of elements with
  higher atomic masses have higher densities than
  minerals made up of atoms with lower atomic
  masses.

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The Properties of Minerals

• Galena contains much lead, which has a relatively
  high atomic mass of 207. Galenas density is
  about 7.5 grams per cubic centimeter.
• Quartz is made up of silicon and oxygen, which
  have relatively low atomic masses of 28 and 16
  respectively. Quartzs density is only about 2.6
  grams per cubic centimeter.

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The Properties of Minerals
Galena
Pyrite
Sulfur
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Density of Minerals

• The density of minerals varies, depending on what
  elements the minerals contain. Samples of the
  minerals in the data table were analyzed for
  density, silicon and oxygen content, and the
  presence of metals. Study the data table and then
  answer the questions.

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Density of Minerals

1. Using Tables Which mineral has the lowest
   density? The highest density?

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Density of Minerals

1. Using Tables Which mineral has the lowest
   density? The highest density? Answer
   quartz olivine

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Density of Minerals

1. Using Tables Which minerals have the lowest
   percentage of silicon and oxygen? Which has the
   highest?

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Density of Minerals

1. Using Tables Which minerals have the lowest
   percentage of silicon and oxygen? Which has the
   highest? Answer olivine and augite
   quartz

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Density of Minerals

1. Formulating Hypotheses Olivine and augite are
   abundant in oceanic crust and in the mantle.
   Quartz, muscovite, and hornblende are abundant in
   continental crust. Formulate a hypothesis to
   explain why continental crust floats higher on
   the mantle than oceanic crust.

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Density of Minerals

1. Formulating Hypotheses Olivine and augite are
   abundant in oceanic crust and in the mantle.
   Quartz, muscovite, and hornblende are abundant in
   continental crust. Formulate a hypothesis to
   explain why continental crust floats higher on
   the mantle than oceanic crust. Answer
   Continental crust is composed of less dense
   minerals than oceanic crust. Therefore,
   continental crust is more buoyant and floats
   higher on the mantle.

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Density of Minerals

1. Drawing Conclusions How is a minerals density
   related to its silicon and oxygen content?
   

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Density of Minerals

1. Drawing Conclusions How is a minerals density
   related to its silicon and oxygen content?
   Answer In general, the higher the
   silicon and oxygen content of a mineral, the
   lower its density.

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The Properties of Minerals

• Hardness
• The atoms of minerals are held together by
  chemical bonds of different kinds and strengths.
• Hardness is the resistance of a mineral to
  scratching.

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The Properties of Minerals

• Hardness
• A hard mineral can scratch a softer mineral.
• The hardness of minerals is ranked on a scale
  from 1 to 10, called Mohs hardness scale.
• Diamond is the hardest mineral, with a hardness
  of 10.
• Talc is one of the softest minerals, with a
  hardness of 1.

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The Properties of Minerals

• Geologists use scratch tests to determine the
  hardness of mineral specimens.
• A glass plate has a hardness of 5.5. A mineral
  that scratches the plate has a hardness greater
  than 5.5.
• A copper penny, which has a hardness of about
  3.5, can scratch talc, but it cannot scratch
  quartz.
• A fingernail, with a hardness of 2.5, and a
  streak plate, with a hardness of 6.5, can also be
  used to test hardness.

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The Properties of Minerals

• Fracture and Cleavage
• The fracture of a mineral is how the mineral
  breaks.
• Fracture is determined by the crystalline
  structure of the mineral and the bonds between
  the atoms in the crystals.

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The Properties of Minerals

• Cleavage is a type of fracture in which the
  mineral tends to split along regular,
  well-defined planes where the bonds are weakest.
• Mica and graphite form sheets. Each sheet
  contains chemical bonds that are very strong.
• The sheets are held together with weak bonds, so
  they can easily be peeled apart from each other.

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The Properties of Minerals

• Mica forms in thin, flat sheets that can be
  easily peeled apart. When halite is broken apart,
  it forms small cubes that show its crystal
  structure.

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The Properties of Minerals

• Other Properties
• Some minerals have unusual properties.
• Acids dissolve calcite easily.
• Magnetite is strongly attracted by a magnet.
• Fluorescent minerals like fluorite give off
  visible light when they are held under an
  ultraviolet light.

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The Properties of Minerals

• Some minerals have unusual electrical properties.
  
• Quartz and tourmaline, for example, become
  electrically charged when heated and cooled or
  subjected to pressure.
• Quartzs electrical properties have applications
  in electronics equipment.

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Assessment Questions

• Which of the following properties would not be
  used to identify an unknown mineral?
• crystal shape
• density
• hardness
• size

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Assessment Questions

• Which of the following properties would not be
  used to identify an unknown mineral?
• crystal shape
• density
• hardness
• sizeANS D