Minerals

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Minerals Ores

• Earth Science
• Chapter 14

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14A Components of Minerals

• Minerals can be made of
• elements a native mineral is made up of
  only one element
• compounds contain atoms in a fixed
  ratio, most minerals are compounds
• mixtures minerals are never mixtures,
  mixtures of minerals are rocks.

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14B Identifying Minerals

• Some minerals have distinctive characteristics
  that make identification easy. Some others share
  characteristics and thus are more difficult to
  identify.
• Properties include color, streak, luster,
  crystal shape, cleavage, hardness, specific
  gravity, flame test, acid test, magnetism,
  radioactivity, glow (UV), refraction.

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Color

• A good first step, but since many minerals share
  the same color, additional tests need to be done.
  
• Exposure to air may cause surfaces to oxidize or
  tarnish.
• Impurities impart different colors. Ex. Quartz
  may be green, pink, blue, violet, milky, or even
  smoky.

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• Iron Ores
• Quartz

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Streak

• Streak is the color of the powder form of the
  mineral.
• A specimen is rubbed across un-glazed porcelain.
• Even if impurities are present, the streak color
  will remain true to the mineral.
• Ex. iron pyrite (fools gold) leaves a greenish
  black streak while real gold leaves a gold streak

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Luster

• Luster is the quality and intensity of the light
  reflected from a minerals surface.
• Some common luster descriptors are metallic,
  glassy, pearly, adamantine (diamond), silky,
  greasy, dull, and resinous.
• Minerals are generally separated into two large
  groups metallic and non-metallic lusters.

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Crystal Shape

• Crystals take their shape from the arrangement of
  the atoms in the mineral.
• Each mineral has a characteristic crystal shape.
  Ex. quartz is hexagonal
• Crystal get larger by adding on base units in a
  process called accretion.
• May also form when molten rock cools. Fast
  cooling small, slow cooling large crystals.

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Cleavage

• Cleavage is the characteristic of some minerals
  to break into flat sheets or along certain
  planes.
• Crystals cleave because some bonds between atoms
  are not as strong as others
• Five Cleavage Ratings perfect, good, fair, poor,
  and none
• Mica perfect to quartz - poor

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Fracture

• Minerals that do not break along cleavage lines
  but seem to have some pattern in their breaking
  have fracture.
• Different types of fracture are
• Conchoidal, fibrous, uneven, and hackly
• Flint is an example of conchoidal fracture,
  asbestos is an example of fibrous, chalcocite is
  an example of uneven.

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• conchoidal
• non-conchoidal

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Hardness

• The ability of a mineral to withstand scratching
  and abrasion is called hardness.
• Friedrich Mohs devised a method for determining
  hardness and it is called the Mohs scale.
• Mineral range for 1 (very soft) to 10 (very hard)
• Talc has a hardness of 1 and diamond has a
  hardness of 10.
• Some everyday tools can be used to determine
  hardness.

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Specific Gravity

• Specific gravity is the ratio of the mass of a
  substance to the mass of an equal volume of water
  at 4C.
• Estimates of specific gravity can be made by
  hefting equal size (volume) samples of mineral
  and comparing.
• Specific gravity is found using water
  displacement.

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Flame Test

• Some minerals produce characteristic colors of
  flame or residue when they burn. This flame test
  can be used to identify minerals.
• Sodium produces a yellow flame
• Potassium produces a violet flame
• Calcium produces an orange-red flame.

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Acid Test

• If an acid, typically hydrochloric acid, is
  applied to certain minerals it causes the mineral
  to fizz, giving off bubbles of carbon dioxide.
• Carbonates, sulfides, and sulfites can be
  identified in this way.

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Magnetism

• Some minerals display magnetism. Some are even
  strong enough to pick up ferrous objects.
• Magnetite, a form of iron ore, was used in early
  compasses and was called lodestone.

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Glow

• Some minerals glow when they are placed under
  ultraviolet light. This occurs because they
  absorb ultraviolet light and emit visible light.
  
• This phenomena is called fluorescence.
• Some emit light when the light source is removed.
  Such minerals are called phosphorescent.

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Refraction

• Some transparent minerals can be identified by
  the way they bend light rays.
• All transparent minerals bend light rays by
  slowing the light rays down.
• Calcite is a good example of a mineral that shows
  double refraction, it produces a double image as
  light passes through it.

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Minerals in NatureNative Minerals

• Native minerals are those found in their pure
  state in nature.
• Examples include gold, silver, copper, platinum,
  diamond, and sulfur.
• Compound minerals are those made from combining
  more than one element.
• Examples include silicates, oxides, sulfides,
  and carbonates.

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Gold

• Gold is found in veins in
  rock or
• in placer
  deposits.
• Placer deposits are
  locations
• where running water has
  separated the very dense gold from other rocks.
• Panning, sluicing, and dredging are ways to
  separate small gold particles from the
  overburden.

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Gold

• Gold is used as currency in
• many places.
• It is also an excellent conductor
• of heat and electricity.
• It is extremely malleable (sheets)
• and ductile (wires).
• It is often found along side silver in
• mineral deposits.
• There are many references to gold and refining
  gold in the Bible.

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Silver

• Silver is more plentiful
  than
• gold and so is less
  expensive.
• It is very good conductor of electricity and so
  is used in electrical circuits and in solder.
• Silver compounds are also
• used in photography.
• Silver is also used to coat
• mirrors because of its high
• reflectance.

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Copper

• Copper is a good
• conductor
  electricity and
• heat.
• It is used extensively in electrical wiring. It
  is also used in plumbing
• applications, especially
• where heat conduction is
• important.
• It is also used in jewelry.

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Platinum

• Platinum is extremely
• resistant to
  corrosion. It is used as a catalyst for certain
  chemical reactions (cars catalytic converter)
• It is more dense than gold and
• because of its rarity, it also
• more expensive than gold.

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Diamond

• Diamond is the hardest
  known
• mineral. It is
  composed of
• pure carbon.
• Diamonds are usually found in the necks of
  extinct volcanoes.
• Diamond is used a coating
• for tool edges to extend
• wear life.
• Diamond crystals are sized using
• carats (a standard of mass for
• gems).

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Sulfur

• Sulfur is
  identified by its
• yellow color
  and
• conchoidal
  fracture.
• Sulfur burns with a blue
• flame.
• Sulfur is often found around
• the vents of volcanoes.
• The Frasch process is used
• to obtain sulfur below the
• surface.

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Silicates

• Silicates are the
  most
• abundant class
  of
• minerals. 90
  of earths
• crust is
  silicates.
• These minerals contain the
• elements silicon and oxygen.
• Quartz is an example of a
• silicate.
• Feldspar is another example
• and happens to be the most
• common mineral in the crust.

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Oxides

• Oxides are minerals composed of oxygen and one
  other element, typically a metal.
• These mineral oxides are often our chief source
  of important metals.
• Hematite is an example of an iron ore,
  cassiterite is a tin ore, and bauxite is an
  aluminum ore.

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Sulfides

• Mineral sulfides are composed of one or metals
  and the element sulfur.
• These contain metals very important to our lives.
• Many have characteristic colors and have colored
  streaks.
• Galena (lead), cinnabar (mercury), and pyrite
  (iron) are some examples.

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Carbonates

• Carbonate minerals contain a metal ion and the
  carbonate ion (carbon oxygen).
• Carbon dioxide is released (fizzing) results when
  an acid is put on a carbonate mineral.
• Calcite dolomite malachite azurite