Download Minerals

Minerals
This is not a spider web. It is
a fractal; a repeating
geometric design
What is a mineral
• A mineral is a natural, inorganic, crystalline solid
• Ask these questions:
– Is it inorganic?
• Only inorganic materials can be minerals
– Organic means it is or was once alive
– Coal is made from dead plants and is organic
– Does it occur naturally?
• Steel is man-made and is not a mineral
– Does it have a crystalline form?
• Petroleum occurs naturally and is inorganic but is not a solid so
it has no crystalline form and is not a mineral
– Does it have a definite chemical composition?
• Mixtures are not minerals; compounds can be minerals
Rocks and the Rock Cycle
•Made of one or more types of
minerals
Types of Minerals
• The most common
minerals are rockforming
• All minerals fall into
two categories:
– Silicate minerals
– Non-silicate minerals
Silicate Minerals
• All silicate minerals contain silicon
(Si) and Oxygen (O) in varying
combinations
– Quartz contains only Si and O
• Feldspar is the most common
silicate mineral
– Different types of Feldspar are formed
when other elements (K, Na, Ca, etc)
are combined with the Si and O
• Feldspar and quartz make up 50%
of the earth’s crust
• Silicate minerals make up 96% of
the Earth’s crust
Non-silicate Minerals
• Only 4% of the Earth’s crust
Crystalline structure
• A crystal is a natural solid with a
definite shape
– A large mineral crystal will display the
characteristic geometry of its crystalline
structure
– Crystals have a specific geometry of
atoms that repeats
– If a mineral is allowed to develop
unrestricted then it will form one, huge
crystal
Crystal Shapes
• Draw Figure 3 on page 107
Mineral identification
• A Mineralogist is a scientist who identifies minerals
• Characteristics:
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Color
Luster
Streak
Cleavage/fracture
Hardness
Crystal shape
Density
Color
• This is probably the worst characteristic to classify
minerals because it is inconsistent
– Some minerals have distinctive colors (Sulfur is yellow,
azurite is blue, serpentine is green)
– Many minerals are similar in color
Color
– Very small amounts of certain element can greatly affect
the color
• Corundum is a colorless mineral made from Aluminum and
Oxygen but with a little bit of chromium it forms a ruby
• Sapphire is corundum with traces of cobalt and titanium
• Amethyst is quartz that has a purple color because of small
amount of Manganese and Iron
Streak
• The color of the mineral
in its powdered form is
called the streak
– This is fairly reliable for
identification
• Metallic minerals have a
dark streak
– Ex. Pyrite (fool’s gold) has
a black streak
• Nonmetallic minerals
have a streak that is
colorless or a very light
shade of the mineral’s
normal color
Cleavage and Fracture
• Cleavage: when a mineral splits evenly along flat
surfaces
– Ex. Micas which split in sheets
– The cleavage runs parallel to a plane in the crystal
where the bonding is weak
– Fracture: when a mineral breaks unevenly
• Curved surfaces are called conchoidal
• Fibrous surfaces look like broken wood
• Rough surfaces are called uneven or irregular
Hardness
• Hardness is the ability of a mineral to resist
scratching
– Ex. A diamond is extremely hard but can easily
be split along cleavage planes
– The hardness of an unknown mineral can be
determined by scratching it against other
minerals of a known hardness on the Mohs
hardness scale
– The hardness of the mineral determines the
strength of the bonds between the atoms
• Graphite and diamonds are made from carbon. Graphite
has no crystal structure so it is not as hard as diamonds
Hardness
• The Moh’s scale is used to determine
relative hardness
• It has hardness values from 1 (softest) to 10
(hardest) with examples of each value
• You can classify the hardness of a mineral
by determining whether or not it will scratch
a mineral with a known value.
– If it will scratch the other mineral, its Moh’s scale
value is larger than that mineral
– If it will NOT scratch the other mineral, its Moh’s
scale value is smaller than that mineral
Crystal Shape
• A certain mineral
always has the same
general shape
because the atoms or
ions that form its
crystals always
combine in the same
geometric pattern
Density
• Density = Mass ÷
Volume
• The density depends on
what type of atoms the
mineral contains and
how closely they are
packed together
– Most of the common
minerals have densities
between 2 and 3 g/cm3
– Heavy metals (gold,
uranium, lead) can have
densities from 7 to 20
g/cm3
Special Properties
• Magnetism
– Magnetite is the most common
• Lodestone is a type of magnetite
that acts like a magnet
• Double Refraction
– Clear minerals still fracture light
that passes through them
creating double images
• Radioactivity
– Some atoms have unstable
protons and neutrons. This
nuclear decay releases energy
• Uranium and Radium are some
radioactive elements that occur
in minerals
• Pitchblende is the most common
uranium containing mineral
Special Properties
• Fluorescence (ability to glow under UV light)
– Calcite is white under normal light but red under
UV light
– Fluorescent minerals absorb UV light and then
produce visible light of various colors
• Phosphorescence (ability to glow under UV
light even after UV light is shut off)
Classwork 1 – Minerals and Rocks
1. Define mineral
2. R___ are made of m____
3. Name the two types of minerals. Which one is
most prevalent on Earth?
4. Name and describe six properties of minerals
that can be used to identify them
5. Name and describe two special properties of
minerals
6. Is steel a mineral? Explain.
Copy the questions into your notebook (right-side) and answer them