Minerals

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Minerals
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So what is a mineral?What are the
characteristics of all minerals?
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Do you Know?
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Mineral Characteristics
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1. A mineral occurs naturally.
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2. A mineral is solid.
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3. A mineral has a definite chemical composition.
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4. A minerals atoms are arranged in an definite
crystaline structure.
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• Of the almost 3000 known minerals, only about 30
  are common.
• The most common are quartz,feldspar,mica, and
  calcite.

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• These minerals make up most of the rocks found in
  the Earths crust.

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• In fact, over 60 of the Earths crust is made up
  of the family of minerals known as feldspar!

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• To be able to identify these and other minerals,
  we need to look at the properties used to
  separate and distinguish these minerals.

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Crystal Systems

• There are six main crystal system
• 1 Cubic or isometric (3 axes of equal length
  intersect at 90)
• 2 Tetragonal (2 axes of same length, all at 90 )
  
• 3 Orthorhombic (3 axes of different length at 90
  )
• 4 Hexagonal (3 horizontal axis at 60. Vertical
  axis at 90)
• 5 Monoclinic (3 axes of different length, 2
  intersect at 90 , the other is oblique to the
  others)
• 6 Triclinic (3 axes of different length are all
  oblique to one another)

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six main crystal system
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Crystallization by cooling from magma

• Whats magma?
• Molten or partially molten rock beneath the
  earths surface
• Magma is generated when rock deep underground
  melts due to the high temperatures and pressures
  inside the earth
• Magma is lighter than the surrounding rock, it
  tends to rise
• -encounters colder rock and begins to cool

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Slow Cooling - bigger minerals with
distinctcrystal structure
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Crystallization through precipitation
Atoms or ions left behind in an evaporating
solution bond with one another to form solids
Halite NaCl forms from evaporation of seawater
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• CLASS Silicate ion SiO44-
• 14 ratio of Silicon to Oxygen and other elements
• most abundant of the minerals (96)
• most common silicates are feldspar and quartz

Both have conchoidal fracture and vitreous luster
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Silicate structure
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Silicate structure
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Silicate structure
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CLASS Carbonate ion CO32- -
contain carbon and oxygen in a 13 ratio and
other metallic elements... calcite and dolomite
are common carbonates
Most react with hydrochloric acid
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• CLASS Oxide ion O22-
• contain oxygen and a metal atom... many
  common ores are oxides, such as hematite and
  magnetite

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Oxide structure
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CLASS Sulfide ion S2-
- contain sulfur and a metal atom... pyrite is
the most common sulfide
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Pyrite (FeS2)
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CLASS Sulfate ion SO42- -
contain sulfur and oxygen in a 14 ratio and a
metal atom
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Sulfate Structure
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CLASS Halides ions Cl-, F-, Br-,
I- - contains chloride or fluoride ions and a
metal atom...halite (table salt) is the most
common halide
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CLASS Native elements ions none, no
charged ions
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Copper (Cu)
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Identifying Minerals

• Remember!
• Rarely is a mineral identified by a single
  property.
• These properties need to be considered together
  to correctly identify a mineral.

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color

• Color is the most easily observed mineral
  property and the least useful!

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color

• Some exceptions to the color rule would be
  cinnabar, which is always red, and malachite,
  which is green.

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color

• Many minerals have a similar color.

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color
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Quiz Break!
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Discuss the following!

• How many of the characteristics of minerals can
  you name?
• Why isnt color a very good property to identify
  most minerals?

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luster

• Luster refers to the way a mineral shines in
  reflected light.
• Notice the difference between these two minerals?

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luster

• There are several terms used to describe
  nonmetallic luster. Examples could be vitreous,
  like the quartz on the left, or pearly, like the
  gypsum on the right.

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• Other terms that might be used include greasy,
  dull, and earthy.
• Can you tell which of these has an earthy luster
  and which has a vitreous luster?

Were you Right?
Vitreous
Earthy
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streak

• Streak of a mineral is the color of its powder
  when rubbed on an unglazed white tile.

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cleavage

• Mica is probably the best example as it splits
  into thin sheets. It is said to have one perfect
  cleavage.

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cleavage

• Feldspar splits readily in two directions, always
  at or near right angles.

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cleavage

• Calcite and galena cleave in three directions.
• They are said to have three good cleavages.

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cleavage

• Not all minerals show cleavage.
• Those that dont break along cleavage surfaces
  are said to have fracture.

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Quiz Break!
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Discuss the following!

• There are four common minerals, how many can you
  name?
• Of the four common minerals, which one makes up
  over 60 of the Earths crust?

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Discuss the following!

• Is the streak of a mineral identical to its
  color?
• What happens to quartz when broken?

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Hardness

• The hardness of a mineral is its resistance to
  being scratched.

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Hardness

• Friedrich Mohs devised a hardness scale.
• In this scale, 10 well known minerals that are
  found in nature and are easily recognizable, are
  given numbers from one to ten.
• We then compare an unknown mineral to those 10

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Hardness

• Talc (left) is the softest and has a hardness of
  1
• Gypsum is a bit harder and has a hardness of 2

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Hardness

• Calcite (left) has a hardness of 3
• Fluorite has a hardness of 4

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Hardness

• Apatite (left) has a hardness of 5
• Feldspar has a hardness of 6

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Hardness

• Quartz (left), with a hardness of 7
• Topaz has a hardness of 8

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Hardness

• Corundum (left) has a hardness of 9
• Diamond with its hardness of 10

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Quiz Break!
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Discuss the following!

• Does this mineral show cleavage or fracture?
• Of the four most common minerals, which is the
  highest hardness?

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crystal shapes

• Crystal shape can be a useful property to
  identify minerals

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specific gravity

• Specific gravity tells you how many times as
  dense as water the mineral is.
• Pure gold can have a specific gravity as high as
  19.3!

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acid test

• Calcite is calcium carbonate, CaCO3. If a drop of
  weak hydrochloric acid is placed on calcite, the
  acid bubbles as carbon dioxide is released.

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Other Special Properties
Magnetic
Malleable
Radioactive
Fluorescence
Taste
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Malleable or Ductile

• Minerals that can be hammered thin or shaped are
  said to show these properties.
• Can you think of a mineral that might be shaped
  or hammered?

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Gold would be a perfect example!
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Magnetic

• Some minerals that contain Iron, are magnetic and
  can be picked up by a magnet.

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Fluorescence

• This is the state of glowing while under a
  ultraviolet light.
• Some minerals even glow once the light is turned
  off!

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Radioactive

• Some minerals, such as this uraninite, are
  radioactive.
• They give off subatomic particles that will
  activate a Geiger counter.

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Taste

• Halite (rock salt) can be identified by its
  taste.
• This practice is not recommended!

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The End