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GEOLOGY
Geology is …
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the study of the Earth’s form and
composition, and both historical and
present changes it continues to experience
Divided into 2 broad areas of study
1. Physical Geology
a)
b)
c)
d)
e)
Rocks and minerals
Igneous Processes
Sedimentary Processes
Metamorphic Processes
Plate tectonics
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Earth’s Interior
Mountain Building Processes
Earthquakes and Fault Systems
2. Historical Geology
a) Geologic Time
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Geologic Time Scale
Stratigraphy
b) Earth’s Origin
c) Prehistoric Life
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Fossils
Paleontology
MINERALS
Minerals …
Are the Building Blocks of Rocks
 Are Naturally Occurring
 Are Inorganic
 Are Solid
 Have a Definite Chemical Structure
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Properties of Minerals
1. Crystal Form

External expression of a mineral’s internal
orderly arrangement of atoms
◦ Minerals are crystalline structures made from a mixture of different
elemental compounds.
◦ The shape of a crystal is based on the atomic structure of these
elemental building blocks.
◦ Atoms within a mineral are arranged in an ordered geometric
pattern called a "motif" which determines its "crystal structure."
◦ A mineral's crystal structure will determine its symmetry, optical
properties, cleavage planes, and overall geometric shape.
◦ The mixture of these compounds becomes the blueprint for how
the crystal will grow.
◦ A crystal's growth pattern is referred to as its "Crystal Habit."
2. Crystal Structure
 Introduction
◦ Symmetry: the periodic repetition of structural
features
 2 types
 Translational symmetry
the periodic repetition of a motif across a length or
through an area or volume
 Point symmetry
the periodic repetition of a motif around a point
Translational Symmetry
Point Symmetry
Point Symmetry Operations
4 different point symmetry operations.
 Reflection
◦ Occurs when a motif on one side of a plane passing through the
center of a crystal is the mirror image of a motif which appears on
the other side of the plane. The motif is said to be reflected across
the mirror plane which divides the crystal.
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Rotation
◦ Arises when a structural element is rotated a fixed number of
degrees about a central point before it is repeated.
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Inversion
◦ Every line drawn through the center of the crystal will connect
two identical features on opposite sides of the crystal.
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Rotoinversion
◦ a compound symmetry operation which is produced by
performing a rotation followed by an inversion.
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32 possible combinations of symmetry operations.
32 crystal classes
Each crystal class is a member of one of 7 crystal systems
◦ Every crystal of a certain crystal system will share a characteristic
symmetry element with the other members of its system.
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A crystal form is a set of planar faces which are
geometrically equivalent and whose spatial positions are
related to one another by a specified set of symmetry
operations.
◦ A simple crystal may consist of only a single crystal form. A more
complicated crystal may be a combination of several different forms.
Lattices and Unit Cells
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A specified motif which is translated linearly and repeated many times
will produce a lattice.
◦ Motif – spatial arrangement of atoms
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A lattice is an array of points which define a repeated spatial entity
called a unit cell.
The unit cell of a lattice is the smallest unit which can be repeated in
3 dimensions in order to construct the lattice.
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Corners of the unit cell that serve as points which are repeated to
form the lattice array are called lattice points.
There are14 different lattices called Bravais lattices
3 - 90o axes
All equal
Copper, Silver,
Sodium Chloride
3 - 90o axes
Only 2 equal
Tin, Rutile,
Spodumene
3 - 90o axes
All unequal
Gallium, Perovskite
3 – axes
One pair not at 90o
Gypsum
3 - axes
None at 90o
Potassium
Chromate
3 – axes equally inclined
None at 90o
All equal
Calcite, Arsenic,
Bismuth
3 - 120o axes coplanar
4th axis at 90o
Zinc, Cadmium,
Quartz
3 – fold axes
4 – fold axes
7 Crystal Systems
The crystal system is a grouping of crystal structures
that are categorized according to the axial system used
to describe their atomic "lattice" structure.
 A crystal's lattice is a three dimensional network of
atoms that are arranged in a symmetrical pattern.
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The seven unique crystal systems, listed in order of decreasing symmetry, are …
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Each crystal system consists of a set of three
crystallographic axes (a, b, and c) in a particular
geometrical arrangement.
1. Isometric (Cubic) - halite, magnetite, and garnet
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The crystallographic axes used in this system are of equal length and
are mutually perpendicular, occurring at right angles to one another.
Can have 2, 3 or 4 fold axes of symmetry
Minerals of this system may demonstrate up to 9 different mirror
planes.
2. Hexagonal – quartz, apatite, beryl
 3 crystallographic axes which intersect at 120° and a
fourth which is perpendicular to the other three.
◦ 4th axis is usually depicted vertically.
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possess a single 6-fold axis of rotational symmetry
up to six 2-fold axes of rotation
up to 7 mirror planes
3. Tetragonal - zircon and cassiterite
 a simple cubic shape that forms a rectangular prism.
 will have a square base and top, but a height which is
taller.
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3 mutually perpendicular axes
possess a single 4-fold symmetry axis
possess up to four 2-fold axes of rotation
up to 5 mirror planes
4. Trigonal (rhombohedral) – calcite, dolomite
 possess a single 3-fold axis of rotation
 possess up to three 2-fold axes of rotation
 up to 3 mirror planes.
5. Orthorhombic - olivine and barite
3 mutually perpendicular axes, each of which is of a
different length than the others
 possess three 2-fold rotation axes
 3 mirror planes
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6. Monoclinic - amphibole, orthoclase
3 unequal axes
2 are inclined toward each other at an oblique
angle
 3rd axis is perpendicular to the other two
 2-fold rotation axis
 a single mirror plane
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7. Triclinic - plagioclase
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3 unequal axes
all intersect at oblique angles
None are perpendicular to the others
only a 1-fold symmetry axis = no symmetry
No mirror planes
3. Luster
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The appearance or quality of
light reflected from the
surface of a mineral
Types of Luster
◦ Metallic – pyrite, galena, gold,
silver
◦ Nonmetallic
 Vitreous (glassy) – quartz,
topaz, fluorite
 Silky – serpentine, ulexite,
satin spar gypsum
 Resinous – garnet, sphalerite
 Earthy – hematite, limonite
Examples of Mineral Luster
Metallic
Vitreous
Nonmetallic
Silky
Resinous
Earthy
4. Color
 Caused by slight impurities in the mineral
 Unreliable diagnostic property
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A mineral can be a variety of colors
Example: Varieties of Quartz
5. Streak
 The color of a mineral in its powdered
form
 More reliable indication of color
 Obtained by rubbing the mineral across a
piece of hard, unglazed porcelain – streak
plate
Appearances can be deceiving
6. Hardness
 A measure of the resistance of a mineral
to abrasion or scratching
◦
One of the most useful diagnostic properties
Determined by rubbing the mineral to be
identified against another substance of
known hardness
MORS Hardness Scale
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Consist of 10 minerals arranged in order from
hardest (10) to softest (1)
7. Cleavage
 The tendency of a mineral to cleave, or
break, along planes of weak bonding
◦
When a mineral breaks evenly in more than
one direction, cleavage is described by the
number of planes exhibited and the angles at
which they meet.
Types of Cleavage
1. Cleavage Quality
a.) perfect – mica, calcite
b.) imperfect – beryl
c.) poor – garnets
a.
b.
c.
d.
e.
f.
g.
2. Crystallographic Type
a.) basal – micas
b.) prismatic – feldspar
c.) cubic – halite, galena
d.) octahedral – fluorite
e.) rhombohedral – calcite
f.) pinacoid – amphibole
g.) dodecahedral – sphalerite
Cleavage in 1 direction – basal
Cleavage in 2 directions at right angles – prismatic
Cleavage in 3 directions at right angles – cubic
Cleavage in 4 directions – octahedral
Cleavage in 3 directions not at right angles – rhombohedral
Cleavage in 2 directions not at right angles – pinacoid
Cleavage in 6 directions – dodecahedral
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Basal
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Prismatic
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Cubic
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Octahedral
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Rhombohedral
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Pinacoid
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Dodecahedral
8. Fracture
 Occurs when a broken mineral has a jagged,
uneven appearance
 Examples
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Concoidal fracture – broken glass: quartz
Subconcoidal fracture – like concoidal but
w/o curved surface:
andalusite
Uneven fracture – uneven surface: anhydrite
Jagged fracture – sharp points or edges: copper
Splintery fracture – fibrous: Chrysotile serpentine
Earth fracture – broken clay-like surface: limonite
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Conchoidal
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Subconchoidal
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Uneven
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Jagged
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Splintery
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Earthy
9. Specific Gravity
 Compares the weight of a mineral to
the weight of an equal volume of water
10. Other mineral properties
 Taste – halite: salty
 Magnetic – magnetite: attracted to magnet
 Texture – talc: soapy feel
graphite: greasy feel
 Optical – calcite: double refraction
 Odor – sulfur: smells like rotten eggs
 Effervesces – calcite: reacts to HCl (fizzes)
 Malleability – copper: can be made into
different shapes
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Magnetic
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Optical
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Effervesces
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Malleability