Chapter 4 Minerals

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Chapter 4 Minerals Section 1 Section 2
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Objectives
What is a mineral?

• Define a mineral.

• Describe how minerals form.
• Identify the most common elements in Earths
  crust.

Vocabulary

• Mineral
• crystal
• magma
• silicate

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What is a mineral?
What is a mineral?

• Earths crust is composed of about 3000 minerals.
  

• Minerals play important roles in forming rocks
  and in shaping Earths surface, and a select few
  have played a role in shaping civilization.

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Mineral Characteristics
What is a mineral?

• A mineral is a naturally occurring, inorganic
  solid with a specific chemical composition and a
  definite crystalline structure.

Naturally Occurring and Inorganic

• That minerals are naturally occurring means that
  they are formed by natural processes.
• All minerals are inorganic, meaning that they
  arent alive and never were alive during any part
  of their existence.

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Mineral Characteristics
What is a mineral?

• Solids with Specific Compositions

• All minerals are solids with definite shapes and
  volumes.
• Each type of mineral has a chemical composition
  unique to that mineral.
• Although a few minerals, such as copper, silver,
  and sulfur, are composed of single elements, the
  vast majority are made from compounds.
• In some minerals, chemical composition may vary
  within a well-defined range.

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Mineral Characteristics
What is a mineral?

• Definite Crystalline Structure

• The atoms in minerals are arranged in regular
  geometric patterns that are repeated again and
  again.
• A crystal is a solid in which the atoms are
  arranged in repeating patterns.

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Mineral Characteristics
What is a mineral?

• Definite Crystalline Structure

• At times and fairly rare, a mineral will form in
  an open space and grow into one large crystal,
  possibly taking the shape of one of the six major
  crystal systems.

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MINERAL CREATION
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Minerals from Magma
What is a mineral?

• Minerals can form from the cooling of magma.

• Magma is molten material found beneath Earths
  surface.

• The type and amount of elements present in the
  magma help determine which minerals will form as
  it cools.
• Small crystals form from rapidly cooling magma
  and large crystals form from slowly cooling
  magma.

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Minerals from Solution
What is a mineral?

• A given volume of water in a solution can
  dissolve only so much of a solid before the
  water becomes saturated.

• If a solution becomes supersaturated, or
  overfilled, with another substance, mineral
  crystals may begin to precipitate, or drop out of
  solution.
• When liquid evaporates from a supersaturated
  solution, the elements remain behind and may
  begin to arrange into crystals.

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Mineral Groups
What is a mineral?

• About 30 minerals are common in Earths crust.

• The most common minerals are often referred to as
  rock-forming minerals because they make up most
  of the rocks found in Earths crust.
• The vast majority of minerals are made up of the
  eight most common elements.

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Mineral Groups
What is a mineral?
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Mineral Groups
What is a mineral?

• Silicates

• Silicates are minerals that contain silicon and
  oxygen, and usually one or more other elements.

• Silicates make up approximately 96 percent of the
  minerals found in Earths crust.
• The most common minerals, feldspar and quartz,
  are silicates.

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Mineral Groups
What is a mineral?

• Silicates

• One silicon atom attaches to four oxygen atoms to
  form a silica tetrahedron, a three-dimensional
  shape structured like a pyramid.

• The basic silica tetrahedron has the ability to
  share oxygen atoms with other tetrahedron
  molecules.
• This allows the molecules to combine chemically
  and structurally in a vast number of ways.

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Mineral Groups
What is a mineral?

• Silicates

• Some possible arrangements formed by silica
  tetrahedrons include single chains, double
  chains, and sheets.

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Mineral Groups
What is a mineral?

• Carbonates

• Carbonates are minerals composed of one or more
  metallic elements with the carbonate compound
  CO3.
• Carbonates are the primary minerals found in
  rocks such as limestone, coquina, and marble.

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Mineral Groups
What is a mineral?

• Oxides

• Oxides are compounds of oxygen and a metal.
• Hematite (Fe2O3) and magnetite (Fe3O4) are common
  iron oxides and good sources of iron.

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Mineral Groups
What is a mineral?

• Sulfides, Sulfates, Halides, Native Elements

• Other major mineral groups are sulfides,
  sulfates, halides, and native elements.

• Sulfides such as pyrite (FeS2) are compounds of
  sulfur and one or more elements.
• Sulfates such as anhydrite (CaSO4) are composed
  of elements with the sulfate compound SO4.
• Halides such as halite (NaCl) are made up of
  chloride or fluoride along with calcium, sodium,
  or potassium.
• A native element such as silver (Ag) or copper
  (Cu) is made up of one element only.

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Mineral Groups
What is a mineral?
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Objectives
Identifying Minerals

• Classify minerals according to their physical and
  chemical properties.

• Identify different types of minerals.
• Discuss how minerals are used.

Vocabulary

• luster
• streak
• hardness
• cleavage

• fracture
• specific gravity
• ore
• gem

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Mineral Identification
Identifying Minerals

• Geologists rely on several relatively simple
  tests to identify minerals.

• These tests are based upon a minerals physical
  and chemical properties.
• It is usually best to use a combination of tests
  rather than just one to identify minerals.

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Mineral Identification

• Color
• Luster
• Texture
• Streak
• Hardness
• Cleavage/Fracture
• Density

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Mineral Identification
Identifying Minerals

• Color

• One of the most noticeable characteristics of a
  mineral is its color.
• Color is sometimes caused by the presence of
  trace elements or compounds within a mineral.
• In general, color is one of the least reliable
  clues to a minerals identity.

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Mineral Identification
Identifying Minerals

• Luster

• Luster is the way that a mineral reflects light
  from its surface.

• Luster is described as being either metallic or
  nonmetallic.
• Metallic luster describes shiny surfaces that
  reflect light like the chrome trim on cars.
• Nonmetallic luster might be described as dull,
  pearly, waxy, or silky.
• Differences in luster are caused by differences
  in the chemical compositions of minerals.

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Mineral Identification
Identifying Minerals

• Texture

• Texture describes how a mineral feels to the
  touch.
• The texture of a mineral might be described as
  smooth, rough, ragged, greasy, soapy, or glassy.

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Mineral Identification
Identifying Minerals

• Streak

• Streak is the color of a mineral when it is
  broken up and powdered.

• Sometimes, a minerals streak does not match the
  minerals external color.
• A minerals streak rarely changes, even if it is
  weathered or its external color varies slightly.

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Mineral Identification
Identifying Minerals

• Hardness

• Hardness is one of the most useful and reliable
  tests for identifying minerals.
• Hardness is a measure of how easily a mineral can
  be scratched.

• German geologist Friedrich Mohs developed a scale
  in which an unknown minerals hardness can be
  compared to the known hardnesses of ten minerals.
  
• Any mineral with a greater hardness than another
  mineral will scratch that softer mineral.

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Mineral Identification
Identifying Minerals

• Hardness

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Mineral Identification
Identifying Minerals

• Cleavage and Fracture

• Minerals break along planes where atomic bonding
  is weak.
• Cleavage is the ability of a mineral to split
  relatively easily and evenly along one or more
  flat planes.

• To identify a mineral by cleavage, geologists
  count the number of cleaved planes and study the
  angle or angles between them.
• Fracture is the ability of minerals to break with
  arclike, rough, or jagged edges.

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Mineral Identification
Identifying Minerals

• Density and Specific Gravity

• Differences in weight are the result of
  differences in density, which is defined as mass
  per unit of volume.
• Density is expressed as a ratio of the mass of a
  substance divided by its volume, or D M/V.
• Density reflects the atomic weight and structure
  of a mineral.
• The most common measure of density used by
  geologists is specific gravity.
• Specific gravity is the ratio of the weight of a
  substance to the weight of an equal volume of
  water at 4C.

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Special Properties
Identifying Minerals

• Special properties of minerals also can be used
  for identification purposes.

• A type of calcite called Iceland spar causes
  light to be bent in two directions, a process
  known as double refraction, when it passes
  through the mineral.
• Calcite (CaCO3) fizzes when it comes into contact
  with hydrochloric acid (HCl).
• Magnetite, an iron ore, is naturally magnetic.
• The mineral sphalerite produces a distinctive
  rotten-egg odor when it is rubbed vigorously
  across a streak plate.

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Mineral Uses
Identifying Minerals

• Minerals are virtually everywhere.

• They are used to make computers, cars,
  televisions, desks, roads, buildings, jewelry,
  beds, paints, sports equipment, and medicines,
  just to name a few uses.

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Mineral Uses
Identifying Minerals

• Ores

• An ore is a mineral that contains a useful
  substance that can be mined at a profit.

• Examples of ores include Hematite, which contains
  the element iron and bauxite, which contains the
  element aluminum.

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Mineral Uses
Identifying Minerals

• Mines

• Ores are removed by underground mining or from
  large, open-pit mines.
• When a mine is excavated, unwanted rock and dirt,
  known as waste material, are dug up along with
  ore.
• If the cost of separating the waste material
  becomes higher than the value of the ore itself,
  then the mineral will no longer be classified as
  an ore because it would no longer be economical
  to mine it.
• The classification of a mineral as an ore may
  also change if the supply of or demand for that
  mineral changes.

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Gems
Identifying Minerals

• Gems are valuable minerals that are prized for
  their rarity and beauty.

• Gems such as rubies, emeralds, and diamonds are
  cut, polished, and used for jewelry.
• In some cases, the presence of trace elements can
  make one variety of a mineral more colorful and
  thus more prized than other varieties of the same
  mineral.