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Matter and Minerals
From the movie: Honey I shrunk the Geologist
Learning Goals: Matter and Minerals
1. Compare and contrast how geologists define the terms
“mineral” and “rock” and describe the relationship between
these two terms.
2. Describe how the different bond type and strengths (e.g.
covalent, ionic, and metallic) between atomic elements can
result in different physical properties.
3. Explain how physical properties (e.g. color, hardness,
luster, etc.) are used for mineral identification
4. Compare and contrast physical properties of different
types of common rock-forming minerals that have a silicaoxygen tetrahedron as their building block.
Minerals: Building blocks of rocks
Definition of a mineral:
• Naturally occurring
• Inorganic solid
• Ordered internal molecular structure
• Definite chemical composition
Definition of a rock:
• A solid aggregate or mass of minerals
Quartz - A Common Mineral
Periodic Table of the Elements
Composition of Elements
Atomic structure
• Central region called the nucleus
– Consists of protons (positive charges) and
neutrons (neutral charges)
• Electrons
– Negatively charged particles that surround
the nucleus
– Located in discrete energy levels called shells
Idealized structure of an atom
Composition of minerals
Chemical bonding
• Formation of a compound by combining
two or more elements
Ionic bonding
• Atoms gain or lose outermost (valence)
electrons to form ions
• Ionic compounds consist of an orderly
arrangement of oppositely charged ions
Halite (NaCl)- An Example of Ionic Bonding
Composition of minerals
Covalent bonding
• Atoms share electrons to achieve electrical
neutrality
• Covalent compounds are generally
stronger than ionic bonds
• Both ionic and covalent bonds typically
occur in the same compound (bonds are
seldom 100% ionic or covalent in
character)
Covalent bonding – sharing of
valence electrons
Composition of minerals
Isotopes and radioactive decay
• Mass number is the sum of neutrons plus
protons in an atom
• An isotope is an atom that exhibits
variation in its mass number
• Some isotopes have unstable nuclei that
emit particles and energy in a process
known as radioactive decay
Structure of minerals
Minerals consist of an orderly array of
atoms chemically bonded to form a
particular crystalline structure
For ionic compounds, the internal atomic
arrangement is primarily determined by
the size of ions involved
Halite (NaCl)
(Packing Related to Cation and Anion Size)
Structure of minerals
Polymorphs
• Two or more minerals with the same chemical
composition but different crystalline structures
• Diamond and graphite are good examples of
polymorphs
– The transformation of one polymorph to another is
called a phase change
– Example: Peanut Butter in a high pressure cell
makes Diamond - or Grandpa, for that matter!
– http://www.lifegem.com/secondary/LifeGemFAQ2006.
aspx#remainsorashes
Diamond & graphite –
polymorphs of carbon
Clicker Question
Given that diamond and graphite are made of the same
element (carbon), why do you think each one has such
different properties?
A. Carbon atoms have different shapes in graphite than in diamond
and thus don’t bond as well
B. Diamond is formed in the mantle under high pressures which
bonds it together more strongly
C. Graphite is formed later in Earth’s history when gravity is lower
D. When diamond is polished into gemstones, it becomes
clearer and harder
E. Diamonds are a girls best friend, which makes them harder to get
Physical properties of minerals
Crystal Form
• External expression of the orderly
internal arrangement of atoms
• Crystal growth is often interrupted
because of competition for space and
rapid loss of heat
• Note this isn’t cleavage!
The mineral garnet often
exhibits good crystal form
Physical properties of minerals
Luster
• Appearance of a mineral in reflected light
• Two basic categories
– Metallic
– Nonmetallic
• Other terms are used to further describe
luster such as vitreous (oily), silky, or
earthy (like dirt)
Galena is a lead sulfide that
displays metallic luster
Physical properties of minerals
Color
• Generally an unreliable diagnostic
property to use for mineral identification
• Often highly variable for a given mineral
due to slight changes in mineral chemistry
• Exotic colorations of some minerals
produce gemstones
• But we use it anyway :-o)
Quartz (SiO2) exhibits a
variety of colors
Question: How would you know all these samples
are the same type of mineral (quartz)?
A)
B)
C)
D)
E)
They have specific colors common only in quartz
They have the same crystal shape, or habit, related to composition + bonding
They reflect light similarly
They were all collected in the same place (in this case a mine)
None of the above
Physical properties of minerals
Streak
• Color of a mineral in its powdered form
• Helpful in distinguishing different forms
of the same mineral
Hardness
• Resistance of a mineral to abrasion or
scratching
• All minerals are compared to a standard
scale called the Mohs scale of hardness
Physical properties of minerals
Cleavage
• Tendency to break along planes of weak
bonding
• Produces flat, shiny surfaces
• Described by resulting geometric shapes
– Number of planes
– Angles between adjacent planes
Three examples of perfect cleavage –
fluorite, halite, and calcite
Micas have perfect cleavage
muscovite
What will happen when Professor Mueller breaks this piece of calcite
with a hammer?
A)
B)
C)
D)
E)
It will shatter into glass-like shards
It will break along cleavage planes into rhomb-shaped pieces
It won’t break, because it is harder than steel
It will produce an electrical current and glow a green color
None of the above
Physical properties of minerals
Fracture
• Absence of cleavage when a mineral is
broken
Specific Gravity
• Ratio of the weight of a mineral to the
weight of an equal volume of water
• Average value is approximately 2.7
• Simply hefting a mineral works too.
Conchoidal fracture - quartz
Physical properties of minerals
Other properties
• Magnetism
• Reaction to hydrochloric acid
• Malleability
• Double refraction
• Taste
• Smell
• Elasticity
The main difference between minerals and rocks is ________.
A. minerals are smaller than rocks
B. people eat rocks in their vitamins, but don’t generally eat
minerals
C. minerals have a particular chemical composition and ordered
internal structure, whereas rocks are more complicated because
they are mixtures of minerals
D. rocks have a particular chemical composition and ordered
internal structure, whereas minerals are mixtures of rocks
E. minerals and rocks are the same thing; there is no major
difference
Clicker Question
You are hiking in Rocky Mountain Natl Park and pick up a
rock. How would you go about identifying minerals in it?
A. Smack it with a hammer
B. Try to estimate its density
C. Look at it with a magnifying glass
D. Try to scratch it
E. All of the above
Classification of Minerals
Nearly 4000 minerals have been
identified on Earth (most of which we
don’t really worry about).
Rock-forming minerals
• Common minerals that make up most of
the rocks of Earth’s crust
• Only a few dozen members
• Composed mainly of the 8 elements that
make up 98% of the continental crust
Classification of Minerals
Silicates
• Most important mineral group
– Comprise most of the rock-forming minerals
– Very abundant due to large amounts of
silicon and oxygen in Earth’s crust
• Basic building block is the silicon-oxygen
tetrahedron molecule
– Four oxygen ions surrounding a much
smaller silicon ion
Silica Tetrahedra (1 Si, 4 O’s)
Classification of Minerals
Silicate structures
• Single tetrahedra are linked together to
form various structures including
– Isolated tetrahedra
– Ring structures
– Single and double chain structures
– Sheet or layered structures
– Complex 3-dimensional structures
Be sure you
can identify
all the minerals
on this chart
Olivene
Pyronene
Amphibole
Biotite
Muscovite
Orthoclase
Plagioclase
Quartz
Clicker Question
The basic building blocks of silicate minerals are…
a. Long chains of silicon atoms
b. A series of SiH2 molecules bonded together
c. A series of SiH4 molecules bonded together
d. A series of SiO2 molecules bonded together
e. A series of SiO4 molecules bonded together
Classification of Minerals
Common Silicate minerals
• Olivine
– High temperature Fe-Mg silicate
(mantle mineral - formed 100’s
km in Earth
– Individual tetrahedra linked
together by iron and magnesium
– Forms small, rounded crystals
with no cleavage
peridot
Classification of Minerals
Common Silicate minerals
• Pyroxene Group
– Single chain structures involving iron and
magnesium
– Two distinctive cleavages at nearly 90 degrees
– Augite is the most common mineral in the
pyroxene group
Classification of Minerals
Common Silicate minerals
• Amphibole Group
– Double chain structures involving a variety of
ions
– Two perfect cleavages exhibiting angles of 124
and 56 degrees
– Hornblende is the most common mineral in
the amphibole group
Hornblende Crystal
Habit and Atomic
Structure
Pyroxene Crystal
Habit and Atomic
Structure
Classification of Minerals
Common Silicate minerals
• Mica Group
– Sheet structures that result in one direction of
perfect cleavage
– Biotite is the common dark colored mica
mineral
– Muscovite is the common light colored mica
mineral
Muscovite mica
Biotite Mica
Classification of Minerals
Common Silicate minerals
• Feldspar Group
– Most common mineral group
– 3-dimensional framework of tetrahedra
exhibit two directions of perfect cleavage at
90 degrees
– Orthoclase (potassium feldspar) and
Plagioclase (sodium and calcium feldspar) are
the two most common members
Potassium feldspar (Orthoclase)
Plagioclase feldspar
Clicker Question
A.
B.
C.
D.
Given the image of granite with four different
minerals. What is the pink blocky mineral?
Quartz
Orthoclase Feldspar
Biotite Mica
Plagioclase Feldspar
Classification of Minerals
Common Silicate minerals
• Clay minerals
– Clay is a general term used to describe a
variety of complex minerals
– Clay minerals all have a sheet or layered
structure
– Most originate as products of chemical
weathering
– Crystals are super small
Clay Minerals
(at high magnification)
Kaolinite
Clay Pit, near Golden, Colorado: Coors (ceramics)
Clicker Question
I am holding a black mineral with a flat, six-sided shape
that cleaves perfectly. This mineral is:
A. Quartz
B. Pyroxene
C. Amphibole
D. Biotite Mica
E. Muscovite mica
Clicker Question
I am holding a dense black blocky mineral that cleaves at
right angles. This mineral is:
A. Quartz
B. Pyroxene
C. Amphibole
D. Biotite Mica
E. Muscovite mica
Clicker Question
I am holding a light colored and light weight (not very
dense) mineral that has elongate, six-sided shape that forms
a point and does not cleave at all (breaks like glass). This
mineral is:
A. Quartz
B. Pyroxene
C. Amphibole
D. Biotite Mica
E. Muscovite mica
Classification of Minerals
Important nonsilicate minerals
• Several major groups exist including
–
–
–
–
–
–
–
Oxides
Sulfides
Sulfates
Native Elements
Carbonates
Halides
Phosphates
Classification of Minerals
Important nonsilicate minerals
• Carbonates
– Primary constituents in limestone and
dolostone
– Calcite (calcium carbonate) and Dolomite
(calcium-magnesium carbonate) are the two
most important carbonate minerals
Important nonsilicate minerals
• Many nonsilicate minerals have economic value
• Examples
– Hematite (oxide mined for iron ore)
– Halite (halide mined for salt)
– Sphalerite (sulfide mined for zinc ore)
– Native Copper (element mined for metal)
Minerals as aesthetic objects
The following minerals are from Peter Bancroft’s spectacular
collection and are intended to illustrate their aesthetic qualities.
You are not responsible for identifying these on an exam!
Many are uncommon and formed in odd geologic
environments. A huge trade show occur in September in
Denver when hundreds of mineral dealers sell these sorts of
specimens.
If you like the specimens
on the following pages
be sure to bring a thick
wallet, or a rich uncle
to the show - they aren’t
cheap!
Phosphophyllite
Apophyliite
Mimetite
End Minerals
Anhydrite
Calcite
Bournonite
Tanzanite
Neptunite
End MineralsEmerald
Opal
(Beryl)
Morganite
Pyromorphite
Gold
Hemimorphite
Apatite
End Minerals
Manganite
Topaz
Silver
Aquamarine
(Beryl)
Wulfenite
The
Crocoite
Quartz on
Hematite
Sulfer
Malachite
Magnetite
Pyrite
Dioptase
Pyrrhotite
Spinel
Diamond
Brazilianite
Legrandite
Pyromorphite
Pyrargyrite
Rhodochrosite
Tourmaline
Sulfer
Stibnite
Cinnnabar
Analcime
Serandite
Quartz
Garnet
Silver
Flourite
Peridot
Azurite
Vivianite
Cuprite
Amethyst
(Quartz)