Chapter 3: Minerals
Atoms
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Atoms – basic building blocks for all earth
materials; consist of 3 basic components:
protons, neutrons, electrons
Atoms combine to form Elements
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Elements – fundamental component that can
not be broken down into other substances by
ordinary chemical processes
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Elements combine to form minerals
General Facts About Minerals
2,000 + minerals have been identified
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A few are “native elements” -- made of only
one element, such as sulfur, gold. copper,
and graphite (carbon)
Most are compounds, especially the silicate
group (Si, O)
Common Minerals
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Of the almost 4000 known
minerals, only about 30 are
common.
The most common are
quartz,feldspar,mica, and calcite.
Common in Rocks
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Quartz
Feldspar (group)
Muscovite (silver white mica)
Biotite (black mica)
Calcite
Pyroxene
Olivine
Amphibole (group)
Magnetite, limonite, and other iron oxides
Pyrite
Native Elements
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These minerals make up most of the rocks
found in the Earth’s crust.
NATIVE ELEMENTS
Gold (Au)
Silver (Ag)
Platinum (Pt)
Diamond (C)
Graphite (C)
Sulfur (S)
Copper (Cu)
Gold
Copper
Silver
Minerals: the building blocks of rocks
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Definition of a Mineral:
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naturally occurring
inorganic
solid
characteristic crystalline structure
definite chemical composition
How do we identify minerals?
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Physical properties:
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Color
Luster
Hardness
Crystal shape
Cleavage
Specific gravity
Other
Physical Properties of Minerals
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Color:
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Most obvious, but often misleading
Different colors may result from impurities
Example:
Quartz
Physical Properties of Minerals
Color:
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Streak – color
of a mineral in
powdered form
(used for
metallic minerals)
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Obtained by scratching
a mineral on a piece of
unglazed porcelain.
Example:
Hematite
Physical Properties of Minerals
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Luster:
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Metallic
example:
Galena
How a mineral surface reflects light
Two major types:
• Metallic luster
• Non-metallic luster
Non-metallic
example:
Orthoclase
Examples of metallic luster
More Examples of Metallic Luster
Pyrite (FeS2)
Galena (PbS)
PYRITE
GALENA
Example of non-metallic luster
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Vitreous--quartz
Example of non-metallic luster
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Silky--example plagioclase feldspar
Non-metallic and metallic luster
–
earthy hematite – metallic hematite
Physical Properties of Minerals
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Hardness:
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How easy it is to scratch a mineral
Mohs Scale of Hardness
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relative scale
consists of 10 minerals, ranked 1 (softest)
to 10 (hardest)
Mohs Scale of
Hardness
• Hardest (10) – Diamond
• Softest (1) – Talc
• Common objects:
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- Fingernail (2.5)
- Copper penny (3.5)
- Wire nail (4.5)
- Glass (5.5)
- Streak plate (6.5)
Physical Properties of Minerals
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Crystal shape (or form):
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Quartz
external expression of a mineral’s internal
atomic structure
planar surfaces are called crystal faces
angles between crystal faces are constant for
any particular mineral
Pyrite
Physical Properties of Minerals
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Cleavage vs. Fracture:
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The way a mineral breaks
– Cleavage: tendency of a mineral to break
along planes of weakness
– Minerals that do not exhibit cleavage are said
to fracture
– Do not confuse cleavage planes with crystal
faces! Crystal faces are just on the surface
and may not repeat when the mineral is
broken.
Physical Properties of Minerals
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Cleavage is described by:
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Number of planes
Angles between adjacent planes.
These are constant for a particular mineral
Physical Properties of Minerals
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Cleavage (1 direction):
Example: mica
Physical Properties of Minerals
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Cleavage (2 directions):
orthoclase
amphibole
Physical Properties of Minerals
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Cleavage (3 directions):
halite
calcite
Physical Properties of Minerals
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Cleavage (4 directions):
fluorite
Physical Properties of Minerals
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Fracture:
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minerals that do not
exhibit cleavage
are said to fracture
smooth, curved
surfaces when
minerals break in a
glass-like manner:
conchoidal fracture
Quartz
Physical Properties of Minerals
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Specific gravity:
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weight of a mineral divided by weight of an
equal volume of water
metallic minerals tend to have higher specific
gravity than non-metallic minerals
Galena
SG=7.5
Quartz
SG=2.67
Specific Gravity
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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!
Physical Properties of Minerals
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Other properties:
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reaction with hydrochloric acid (calcite fizzes)
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taste (halite tastes salty)
feel (talc feels soapy, graphite feels greasy)
magnetism (magnetite attracts a magnet)
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Mineral Groups
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Rock-forming minerals
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~30 common minerals make up most rocks in
Earth’s crust
Composed mainly of the 8 elements that
make up over 98% of the crust
Mineral Groups
Element Abundances
SILICATES
Silica
(SiO4)4-
Common cations that
bond with silica anions
All others:
1.5%
Mineral Groups
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Silicates (most abundant)
Non-silicates (~8% of Earth’s crust):
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Oxides
Carbonates
Sulfides
Sulfates
Halides
Native elements
O2(CO3)2S2(SO4)2Cl-, F-, Br(single elements; e.g., Au)
Mineral Groups – Silicates
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Silicates
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Tetrahedron
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fundamental
building block
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4 oxygen ions
surrounding a
much smaller
silicon ion
Silicon-oxygen
tetrahedron
(SiO4)4-
Minerals can have the same chemical composition
(Carbon) but different physical properties because of
their crystal structure
Diamond
Graphite