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Minerals of Earth’s Crust
Chapter 5
What is a mineral?
A natural, usually inorganic solid that has a
characteristic chemical composition, an orderly
internal structure, and a characteristic set of
properties
Halite
Characteristics of Minerals
1. Inorganic
2. Forms and exists in
nature
3. Crystalline solid
(atoms are arranged
in a regular pattern)
4. Consistent chemical
composition
Gypsum
Fluorite
Mineral or Nonmineral?
Mineral or Nonmineral?
Ice?
Salt?
Sugar?
Charcoal?
Rock?
Kinds of Minerals
• Scientists have identified 3,000 minerals
• Of those minerals, there are 20 common rockforming minerals
• All minerals are divided into 2 main groups:
Silicate and Nonsilicate Minerals
Silicates
Nonsilicates
Silicate Minerals
• Minerals that contain a combination of silicon and oxygen
atoms
• Silicate minerals other than quartz have one or more
additional elements such as Ca, Na, K, Fe, or Mg
• Silicate minerals make up 96% of Earth’s crust
• Quartz and feldspar make up more than 50% of the crust
Nonsilicate Minerals
• Minerals that do not contain a combination of
silicon and oxygen atoms
• Nonsilicate minerals make up 4% of Earth’s crust
• There are 6 major classes of nonsilicate minerals
Classification of Nonsilicate Minerals
How to Identify Minerals
Mineralogists identify minerals based on a
number of specific physical properties:
Color
Streak
Luster
Cleavage and Fracture
Hardness
Crystal Shape
Density
Color
• Easy to observe
• Unreliable on its own
• Trace amounts of
certain elements can
greatly effect color of
some minerals (ex:
sapphires and rubies)
• Weathering can also
cause changes in color
Rubies are cut from corundum
with traces of Chromium (Cr)
Sapphires are cut from corundum
with traces of Cobalt (Co)
Streak
• Color of the mineral
in the powder form
• More reliable than
color
• Use a streak plate:
unglazed tile
• Minerals that are
harder than the streak
plate will leave no
streak
Luster
• Light reflected from the mineral’s surface
• Metallic luster reflect light like polished metals
• All other minerals have nonmetallic luster:
waxy, pearly, glassy, dull/earthy, or
virtuous/brilliant
Cleavage and Fracture
• Cleavage is the
tendency of a mineral
to split along specific
planes of weakness to
form smooth, flat
surfaces
• Cleavage occurs in
one, two, or three
directions
Cleavage in three directions. Example: CALCITE
Cleavage and Fracture
• Fracture is when the
mineral does not split
along cleavage planes
• Fracture can be
irregular, fibrous, or
conchoidal
Hardness
• A measure of the ability
of a mineral to resist
scratching
• Hardness does NOT mean
resistance to cleavage
planes!!
• Hardness relates to the
strength of bonds between
the minerals atoms (Ex:
Diamond vs. Graphite)
Moh’s Hardness Scale
• To determine an unknown mineral’s hardness, you
need to scratch it against a mineral of known
hardness
Crystal Shape
• A mineral always has the same basic crystal shape
because the atoms that make up the mineral
always combine in the same geometric pattern
• There are 6 basic crystal systems that can become
more complex due to conditions during formation
Density
• Ratio of mass to volume
of a substance
Density = mass/volume
• Helps identify heavier
minerals more readily
than it helps identify
lighter ones
• Most minerals have a
density between 2 and
3 g/cc
Lead
Density = 11.35 g/cc
Galena
Density = 7.6 g/cc
Special Properties of Minerals
Some minerals
exhibit special
properties that can
also be used for
identification such as:
 Fluorescence
 Phosphorescence
 Double Refraction
 Magnetism
 Radioactivity