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Eric Christiansen
Minerals
Substance of the Earth
• Letters
Elements
• Words
Minerals
• Sentence
Rocks
• Paragraph
Outcrop, mountain, volcano
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The Nature of Minerals
• Mineral
– A naturally occurring inorganic solid that has a
fixed chemical composition with an
orderly internal arrangement of atoms.
Elements
• Minerals are made of elements
• Elements are made of Atoms
– The smallest unit of an element
that retain its properties
– Small nucleus of protons and
neutrons
– Surrounded by a “large” cloud of
electrons
The Nucleus
• Protons
– Positive electrical charge
– Mass equal to 1 atomic unit
• 1 atomic unit = 1.66 * 10-24g
– The number of protons in
the nucleus determines the
atomic number
The Nucleus
• Neutrons
– Electrically neutral
– Mass of 1 atomic unit
• The number of neutrons plus
protons equals the atomic mass
• The number of neutrons in the
nucleus of may vary producing
isotopes but the number of
protons does not change in a
single element
Electrons
• Electrons form clouds around
nucleus
– Negative electrical charge
– Mass is much less than 1
• Not a significant contribution to the
mass of the atom
– Number of Electrons = Protons
in electrically neutral atom
– Loss or gain of electrons
produce ions
Ions
• Atoms may gain or lose
electrons
– Noble gas electron structure
– Loss of electrons makes a
positively charged ion +cation
– Gaining electrons makes a
negatively charged ion -anion
– Oppositely charged ions may
attract one another to make a
chemical bond
Periodic Table of the Elements
Each of the 92 elements has a different number of protons
in its nucleus. There are only about 10 elements that are
abundant and therefore common in minerals.
Fig. 3.3
Periodic chart: Element
Properties
• Atomic number
– Protons
• Charge
– Lost (or gained
electrons)
• Ionic radius
Bonding
• Atoms are stable when their outermost
electron shell is filled
– Electron structure like a noble gas
– Atoms lose, gain or share electrons to
achieve a noble gas structure
• Types or bonds
– Ionic
Covalent
Metallic
Bonding
• Ionic bonds
– Formed between ions of opposite charge
• Covalent bonds
– Atoms share electrons to achieve noble gas
structure
– Very strong compared to most ionic bonds
• Metallic bonds
– Outer electrons are mobile
– Electrical conductivity high
Ionic Bonding
Fig 3.4A
Covalent Bonding
Fig 3.4B
States of Matter
• Solid
– Crystalline - atoms
bond
together in a regular orderly pattern
– Amorphous – atoms in a random pattern
• Liquid - atoms or molecules tightly packed
but in random motion
• Gas - particles in random motion at high
speeds, separated by empty space
The Nature of Minerals
• Mineral
– A naturally occurring inorganic solid that has a
fixed chemical composition with an
orderly internal arrangement of atoms.
Minerals
• Must be solid
• Ice vs. liquid water
• A fixed chemical composition
• Ice vs. seawater
• An orderly internal arrangement of
atoms
• Quartz versus glass (or obsidian)
• Must be formed by a natural process?
• Synthetic diamonds and other gemstones would not be minerals
• Must be an inorganic compound?
• Coal is not a mineral by this standard.
Minerals
• Internal structure
– Repetitive geometric pattern of atoms
– Expressed in physical properties
• Crystal shape
• Cleavage
Polymorphism
• Same elemental
composition but
different structure
• Different physical
properties
Fig 3.17
Common Polymorphs:
Calcite and Aragonite
Calcite=CaCO3
Aragonite=CaCO3
Minerals
• Definite composition
– Chemical composition expressed as a
chemical formula
– Composition ranges from simple to
complex
• Native copper - Cu
• Biotite - K(Mg,Fe)3AlSi3O10(OH)2
– Ionic substitution may occur causing
small variations in composition
Physical Properties of Minerals
1. Crystal Form
2. Density
3. Cleavage
4. Fracture
5. Hardness
6. Color
7. Streak
8. Luster
Discussed
more in lab
Physical
Properties
• Density
– Ratio of mass to
volume
– Common rockforming minerals
range from 2.6 to
3.4 grams/cm3
Pyrite 5.0 g/cm3
K feldspar 2.6 g/cm3
Physical Properties
• Crystal faces &
form
– Growth in
unrestricted
environment
– Form reflects
symmetry of
internal structure
Quartz crystals—
faces are not cleavage
surfaces
Physical Properties
• Cleavage
– Breakage along parallel planes of
weakness
– Related to internal structure -weaker
bonds
– May occur in 1 or more planes
– Fracture is uneven breakage - no natural
planes of weakness
Cleavage Planes
Fig. 3.9 A & D
Mineral Stability
• Stability ranges
– Range of pressure, temperature and
composition under which a mineral forms
– Stable
• Exists in equilibrium with its environment
– Metastable
• A mineral existing outside its stability range
Stability Ranges for SiO2
Fig 3.11
Silicate Minerals
• Most common minerals on Earth
– Comprise 95% of the volume of the crust
– Approximately 75% of the Earth’s mass
is made up of silicon and oxygen
– All silicate minerals are based on the
silica tetrahedron
• SiO4-4
Silicon-Oxygen Tetrahedron
All silicate minerals are based
on the silica tetrahedron
SiO4-4
Fig 3.18
Silicate Minerals
• Silica tetrahedron may polymerize to
form a variety of geometric structures,
alone or in combination with other
cations
• Isolated tetrahedra
• Single chains of tetrahedrons
• Double chains
• 2-D sheets
• 3-D frameworks
Silicate
Minerals
Amphibole
Olivine
(Hornblende)
Pyroxene
Clay’s & Mica
Fig 3.19
Quartz
Feldspars
Silicate
Structures
Chain
Double
chain
Isolated
Sheet
Framework
Fig 3.19
Minerals
• Internal structure
– Repetitive geometric pattern
of atoms
– Expressed in physical
properties
Fig 3.17
Rock-Forming Minerals
• About 20 common minerals make up
most rocks
– Silicates dominate (95% of crust)
– Quartz, Plagioclase feldspar, K-feldspar, Micas,
Amphiboles, Pyroxenes, Clay
– Carbonates are common
– Evaporite minerals
– Secondary minerals formed during weathering
Felsic Minerals
• Silicate minerals rich in silicon and aluminum
–
–
–
–
Relatively low densities
Low crystallization temperatures
Framework structures
Generally light colors
• Feldspars
• Potassium feldspar (~2.5 g/cm3)
• Plagioclase feldspar (~2.6 g/cm3)
• Quartz (2.65 g/cm3)
• Mica – muscovite (2.8 g/cm3)
Feldspar
Plagioclase
• (Ca,Na)(Al,Si)4O8
– CaAl2Si2O8
– NaAl2Si3O8
K-feldspar
• (Na,K)Al2Si3O8
– KAlSi3O8
– NaAlSi3O8
Feldspar
Plagioclase
• (Ca,Na)(Al,Si)4O8
K-feldspar
• (Na,K)Al2Si3O8
– CaAl2Si2O8
– NaAl2Si3O8
– KAlSi3O8
– NaAlSi3O8
• Ca and Na Ions exchange
for one another
Why?
• K and Na Ions exchange for
one another
Feldspar
Plagioclase
• (Ca,Na)(Al,Si)4O8
• CaAl2Si2O8
• NaAl2Si3O8
• Ca and Na Ions exchange
for one another
• Size and Charge Similar
K-feldspar
• (Na,K)Al2Si3O8
• KAlSi3O8
• KAlSi3O8
• K and Na Ions exchange for
one another
• Size and Charge Similar
Ionic Substituion: Size and Charge
Ionic sizes and charges
Feldspar
Plagioclase
• (Ca,Na)(Al,Si)4O8
• CaAl2Si2O8
• NaAl2Si3O8
• Ca and Na Ions exchange
for one another
• Size and Charge Similar
K-feldspar
• (Na,K)Al2Si3O8
• KAlSi3O8
• KAlSi3O8
• K and Na Ions exchange for
one another
• Size and Charge Similar
Feldspars are most common mineral in the
oceanic and continental crust.
Why?
Quartz
SiO2
• Very little chemical
substitution for Si (or
oxygen)
• But many different colors
from trace concentrations
and tiny flaws in crystals
• Chemically unreactive
• Made of light elements
• Density 2.65 g/cm3
02_10.JPG
Mafic Minerals
• Silicate minerals rich in
magnesium (ma-) and iron (-fic)
– Relatively high density and higher crystallization
temperatures
– Generally dark colors
– Olivine (~4.0+ g/cm3)
– Pyroxenes (~3.4 g/cm3)
– Amphiboles (~3.4 g/cm3)
– Mica – biotite (~2.8-3.2 g/cm3)
Why are mafic minerals more dense
than felsic minerals?
Mafic Minerals
Olivine
(~4.0+ g/cm3)
Pyroxene
(~3.4 g/cm3)
Amphibole
(~3.4 g/cm3)
Clay Minerals
• Sheet silicates similar
to mica
• Products of chemical
weathering near the
Earth’s surface
• Usually microscopic
crystals
– Kaolinite
SEM photograph of clay crystals from the Watahomigi Formation in Andrus
Canyon, Supai Group, Grand Canyon; x 20,9000 . U.S. Geological Survey
Professional Paper 1173.
Where are these
minerals found?
• Continental crust
– Plagioclase, K-feldspar,
quartz, mica, amphibole,
pyroxene
• Oceanic crust
– Plagioclase, pyroxene,
olivine
• Mantle
– Olivine, Pyroxene
• Core
– Metallic iron
Nonsilicate Minerals
• Carbonates
• Calcite - CaCO3
• Dolomite - CaMg(CO3)2
• Oxides - Hematite (Fe2O3) Magnetite (Fe3O4)
•
•
•
•
Sulfates - Gypsum - CaSO4-2H2O
Sulfides – Pyrite – FeS2
Halides - Halite - NaCl
Native Elements
• Gold, Silver, Copper, Sulfur, and Carbon
Nonsilicate Minerals
• Carbonates Sedimentary solutions
• Oxides - Hematite Magnetite
•
•
•
•
Sulfates – Gypsum
Sulfides – Pyrite
Halides – Halite
Native Elements
Lots of different rocks
Sedimentary solutions
Metallic ore deposits
Sedimentary solutions
• Gold, Silver, Copper, Sulfur, and Carbon
Cleavage versus Fracture
Sedimentary
solutions
• Crystallize directly
from water
• Carbonates
• Gypsum
• Halite
What is a rock?
• A naturally occurring combination of one
or more minerals
Granite
Which
minerals
are mafic?
More Physical Properties
• Luster
– The appearance of reflected light
– Influenced by the bonding
• Metallic luster, shines like metal
• Non-metallic, ranging from bright to dull
fluorescence
•Magnetism
Characteristic
of only a few
minerals
•Acid (HCl)
Calcite (CaCO3)
Physical Properties
• Hardness
– Not Density
– Resistance to abrasion
– Strength of atomic
bonds holding solid
together
– Mohs hardness scale
– Arbitrary relative numbers
assigned to 10 common
minerals
• Scale is not linear
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Physical Properties
• Hardness
– Resistance to
abrasion
– Strength of atomic
bonds holding
solid together
• Mohs hardness
scale
• Arbitrary relative
numbers assigned
to 10 common
Physical Properties
• Color
– Most obvious property
– Not diagnostic for ID purposes
– Variations due to trace elements
• Streak
– Color of mineral powder
– Diagnostic property
Hematite Colors & Streak
02_08.JPG
(quality of reflected light)
Physical Properties: Luster
• The appearance of
reflected light
– Influenced by the type of
bonding in the mineral
– Metallic luster
• Shines like metal
– Non-metallic
• Widely ranging
from bright to dull
Physical Properties
• Magnetism
– Characteristic of only a
few minerals
• Iron bearing minerals
– Magnetite
– An important property
of rocks in geophysical
investigations of the
Earth
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