Minerals

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Materials of the Earth

• Minerals

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Minerals are..

• Naturally occurring
• Inorganic (non-living)
• Solid
• Composed of elements or compounds
• Definitions that you may or may not know
• Elements are composed of only one type of atom.
• Compounds are 2 or more elements chemically
  combined

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Physical Properties...

• Are the result of the internal arrangement of
  atoms within the mineral.

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Physical Characteristics include...

• Color
• Luster
• Fracture and cleavage
• Streak
• Hardness
• Mineral shape (habit)
• Specific Gravity

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Color

• Color of some minerals is a very useful
  characteristic to use in identifying them. This
  sulfur for example is almost always yellow.

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However, color can be altered by the presence of
small amounts of chemical impurities, so...

• Color should not be relied on too heavily as an
  identifying characteristic for most minerals. For
  example, agate shows that quartz can occur in
  many different colors

Agate is a variety of quartz
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Color is never good for the identification of
Fluorite. These are all samples of fluorite.
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Luster

• Luster is the way in which a mineral reflects,
  refracts, or absorbs light.in other words the
  way that it shines.
• For our purposes, luster may be metallic or
  non-metallic.

Pyrite has metallic luster.
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Non-metallic Luster

• Non-metallic luster means the mineral does not
  have a brilliant shine.
• Non-metallic luster can include such descriptions
  as earthy, pearly, glassy, dull, or silky.

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Metallic Luster

• Metallic luster shines brilliantly.
• When in doubt, ask yourself, does this mineral
  shine like a chrome faucet?

This mineral naturally formed into this shape and
luster.
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Fracture and Cleavage

• Refers to the way in which a mineral breaks.
• If the mineral breaks along smooth flat surfaces,
  it is said to cleave or to have cleavage.

Galena has obvious cleavage.
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• Fracture refers to the characteristic of breaking
  along rough irregular surfaces.
• Minerals like quartz are said to fracture.
• .

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Streak

• Streak is the color of the powder left behind
  when the mineral is gently rubbed on a piece of
  unglazed porcelain.

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Hardness

• Hardness is a minerals resistance to being
  scratched.
• A numerical scale from 1-10 is used to measure
  hardness. (Mohs Scale)
• Talc is the softest mineral at 1.
• Diamond is hardest (10)

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Hardness
1st Attempt to scratch the mineral with you thumb
finger nail. If the mineral is scratched, the
mineral is not as hard as your finger nail, which
has a hardness 2.5 on the Mohs scale.
2nd If the mineral is not scratched by the finger
nail, then gentle attempt to scratch a piece of
glass with the mineral. Try different edges to
be sure. Glass has a hardness of 5.5, so if the
mineral scratches the glass its hardness is
greater than 5.5 on the Mohs scale.
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Crystal shape

• The shape of a mineral crystal is determined by
  the arrangement of its atoms. Each mineral tends
  to occur in a limited number of crystal shapes.

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Aquamarine Beryl Gypsum Fluorite in Galena
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Specific Gravity

• Specific gravity is the ratio of a minerals mass
  compared to an equal volume of water. In other
  words, how many times heavier is the mineral than
  the same amount of water?

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Common Mineral Groups...

• Silicates -
• The 2 most abundant elements in the earths
  crust are oxygen and silicon.
• These combine to form an atomic structure called
  a tetrahedron.
• These tetrahedra form minerals called silicates.

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Carbonates

• A group of minerals in which carbon and oxygen
  combine to form a carbonate CO3 molecule.
• The test for these is the bubble test. When
  exposed to hydrochloric acid they release CO2 and
  they bubble.

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Carbonate and silicate minerals have been found
in abundance on the surface of Mars. Below is
the rover called Spirit as it travels over the
Martian surface taking rock samples.
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Questions to further help your understanding of
minerals

• Hardness is probably the most important
  identifying property of a mineral. Describe the
  process for determining the hardness of a
  mineral. List some common items and their
  harnesses that can be used to help.
• http//www.rockhounds.com/rockshop/hardness1.html

2. Why is the color of a mineral not always a
reliable property for identification? (hint
see earlier slide)
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Questions to further help your understanding of
minerals
3. Write down three specific physical properties
that you can observe for each of the minerals
below.
A
B
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Use your ESRT to identify these minerals.
4. What mineral has nonmetallic luster, easily
scratched by a finger nail and a greenish color?
B
Talc
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Use your ESRT to identify these minerals.
5. What mineral has metallic luster, scratches
glass and shows fracture and is an ore for sulfur?
Pyrite
B
6. What mineral has nonmetallic luster, scratches
glass, has cleavage, is white and shows
striations?
Plagioclase Feldspar