Minerals
What is a mineral?
• With a partner, discuss what you think a
mineral is. Come up with a definition to
share with the class.
• Can you name any minerals?
Which of these are minerals?
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Table Salt
Gold
Zinc
Chlorophyll
Silver
Talc
Diamonds
Minerals are natural compounds formed
through geological processes. The term
"mineral" encompasses not only the
material's chemical composition, but also
the mineral's structure. Minerals range in
composition from pure elements and
simple salts to very complex silicates with
thousands of known forms. The study of
minerals is called mineralogy.
• A mineral must have:
– Crystal Structure: The particles line up in a unique
pattern that repeats over and over again
• The repeating pattern forms a crystal that has definite
flat sides called faces that meet a sharp edges or
corners
– Definite Chemical Composition: A mineral always
contains the same elements in the same proportion
• These elements bond together to form compounds in
which the element lose their identities
Between 2500 and 3000 minerals have
been identified, but there are only 60 that
you will come across in the field. They are
identified by their various physical
properties
Physical Properties of Minerals
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Color
Streak
Hardness
Mineral Cleavage
Fracture
Luster
Color
• Color is one of the most eye-catching
feature of many minerals. Some minerals
always have the same color, such as gold,
whereas some minerals, such as quartz
and calcite, come in all colors.
• Color alone will not normally identify a
mineral, but it can be a very helpful factor.
Streak
• The streak made by a mineral is often a
different color than the mineral itself. The
streak is found by rubbing the mineral on
an unglazed piece of ceramic tile. The
color of the streak is important in helping
you identify the mineral.
Hardness
• Another important factor in knowing your
rocks is the hardness. A common
system of measuring hardness is the
Mohs Scale. The scale runs from the
softest mineral, talc, as "Mohs 1" to the
hardest mineral, diamond, as "Mohs 10".
• Your fingernail has a hardness of 2.5. If
you can scratch your mineral or rock
with your fingernail, you know it is softer
than 2.5. A pocket knife has a hardness
of 5.5. If a mineral cannot be scratched
by your fingernail, but can be scratched
by a pocketknife, you know the
hardness is between 2.5 and 5.5.
Mineral Cleavage
• In mineral terms, cleavage describes how
a crystal breaks when subject to stress. If
the mineral breaks along smooth, flat
surfaces, the mineral cleaves.
Fracture
• In mineral terms, fracture describes how a
crystal breaks when subject to stress. If
the mineral breaks along rough edges, the
mineral fractures.
Luster
• Another important thing to notice when
identifying a mineral is the shine – known
as luster – whether it looks like metal
(metallic) or glass, like diamond or silky.
Video
• What exactly are minerals?