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Minerals
Objectives
• Define a mineral as an Earth material
• Define physical properties that
characterize minerals
• Use physical properties to identify
common rock-forming minerals
Objectives
• Define a mineral as an Earth material
• Define physical properties that
characterize minerals
• Use physical properties to identify
common rock-forming minerals
Minerals
• Comprise 99% of Earth’s crust
• Basic geologic material of the Earth
Table salt, halite
What is a Mineral?
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Naturally occurring
Made by non-human
processes
Crystalline solid
Have a specific chemical composition
Inorganic
What is a Mineral?
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There is a repeatable
Naturally occurring
and orderly structure,
Crystalline solid
which forms a solid.
Have a specific chemical composition
Inorganic
What is a Mineral?
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Naturally occurring
Crystalline solid
Have a specific chemical composition
Inorganic
Molecular composition
expressed using a
chemical formula may allow for some
unknowns
What is a Mineral?
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Naturally occurring
Crystalline solid
Have a specific chemical composition
Inorganic
Formed by Earth
processes, rather than
biological processes
Source material may be
derived from biological
processes, such as
shells
How do minerals form?
• A process called Crystallization:
Atoms come together in the proper
chemical proportions and ordered threedimensional arrangement and grow a solid
from gas or liquid
Minerals are the building blocks of
most crustal rocks
• There are about 9 elements found in large
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abundance in Earth’s crust (Oxygen, Silica,
Aluminum, Iron, Calcium, Sodium, Potassium,
Magnesium, Titanium)
Leading to the 30 most commonly encountered
rock-forming minerals
Although there are thousands of known minerals
geologists commonly encounter only about 30 of
them…
It is important to be able to identify
common rock-forming minerals in order
to then be able to identify rocks in the
field
Remember, there is a huge difference
between minerals and rocks
Next slide shows an example of common
rock-forming minerals producing a granite
rock
Orthoclase
feldspar
Quartz
Biotite
Plagioclase
feldspar
Plagioclase feldspar
Orthoclase feldspar
Rocks are naturally
occurring aggregates
of minerals.
Biotite
Quartz
Granite
Some common rock-forming
minerals
Igneous
Rocks
Quartz
Feldspar
Mica
Pyroxene(Augite)
Amphibole
Olivine
Sedimentary
Rocks
Quartz
Feldspar
Clay minerals
Calcite
Dolomite
Gypsum
Halite
Metamorphic
Rocks
Quartz
Feldspar
Mica
Garnet
Pyroxene
Objectives of Lab Exercise
• Define a mineral as an Earth material
• Define physical properties that
characterize minerals
• Use physical properties to identify
common rock-forming minerals
Mineral Identification Properties
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Hardness
Crystal Form
Cleavage
Fracture
Color
Streak
Luster
Others
Mineral Identification Properties
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Hardness
Crystal Form
Cleavage
Fracture
Color
Streak
Luster
Others
Resistance to abrasion
Reflects strength of
chemical bonds
between atoms
Mineral Identification Properties
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Hardness
Crystal Form
Cleavage
Fracture
Color
Streak
Luster
Others
Mineral
Mohs
Hardness
Talc
1
Gypsum
2
2.5
3
4
5
5.5
6
6.5
7
8
9
10
Calcite
Fluorite
Apatite
Orthoclase
Quartz
Topaz
Corundum
Diamond
Common
Object
Fingernail
Copper
Glass or knife blade
Steel file (varies)
Mineral Identification Properties
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Geometric shape of
Hardness
crystals when grown in
Crystal Form
an unconfined space
Cleavage
Reflects geometric
Fracture
arrangement of the
Color
atoms
Streak
Single crystals --> cubes, prisms, rhombohedrons,
dodecahedrons, tabular, acicular
Luster
Crystal masses --> granular masses, crystalline masses,
botryoidal masses
Others
Mineral Identification Properties
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Hardness
Crystal Form
Cleavage
Fracture
Color
Streak
Luster
Others
How minerals break
(determined by
observation, not
breaking)
Mineral Identification Properties
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Hardness
Crystal Form
Cleavage
Fracture
Color
Streak
Luster
Others
Breakage in a planar
fashion, broken
surfaces are flat
Described according to
how many different
“directions” of
cleavage there are
and how “good” the
cleavage is (I.e., how
smooth the surface is)
Mineral Identification Properties
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Hardness
Crystal Form
Cleavage
Fracture
Color
Streak
Luster
Others
Reflects weaker
molecular cohesion
along cleavage planes
Can be confused with
crystal form
Mineral Identification Properties
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Hardness
Crystal Form
Cleavage
Fracture
Color
Streak
Luster
Others
mica:
1 cleavage
plane
Grotzinger et al. © 2007 by W.H. Freeman & Company
Grotzinger et al. © 2007 by W.H. Freeman & Company
Mineral Identification Properties
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Hardness
Crystal Form
Cleavage
Fracture
Color
Streak
Luster
Others
Grotzinger et al. © 2007 by W.H. Freeman & Company
orthoclase feldspar:
2 cleavage planes
Mineral Identification Properties
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Hardness
Crystal Form
Cleavage
Fracture
Color
Streak
Luster
Others
Breakage in a
nonplanar fashion,
broken surfaces are:
Rough --> “irregular
fracture”
Curved or Rounded -->
“conchoidal fracture”
Pointed --> “hackly
fracture”
Mineral Identification Properties
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Hardness
Crystal Form
Cleavage
Fracture
Color
Streak
Luster
Others
Conchoidal Fracture
Oregon Obsidian
© Public Domain http://en.wikipedia.org
Obsidian Arrowhead
© Public Domain http://en.wikipedia.org
Mineral Identification Properties
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Hardness
Crystal Form
Cleavage
Fracture
Color
Streak
Luster
Others
Pigment of “fresh”
mineral surface in
white light
“fresh” --> clean and
untarnished
It is highly variable
and unreliable alone
Mineral Identification Properties
COLOR is highly variable and unreliable alone
amethyst
milky quartz
©1995-2006 by Amethyst Galleries, Inc.
rose quartz
© 1998-2003 Gem & Mineral Miners, Inc.®
© StoneTrust, Inc.
jasper
© 1998-2003 Gem & Mineral Miners, Inc.®
citrine
rock crystal
© 1998-2003 Gem & Mineral Miners, Inc.®
© 1998-2003 Gem & Mineral Miners, Inc.®
Mineral Identification Properties
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Hardness
Crystal Form
Cleavage
Fracture
Color
Streak
Luster
Others
Color of mineral in
powdered form on an
unglazed porcelain
plate (“streak plate”)
More reliable than color
Grotzinger et al. © 2007 by W.H. Freeman & Company
Mineral Identification Properties
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Hardness
Crystal Form
Cleavage
Fracture
Color
Streak
Luster
Others
How a fresh mineral surface
reflects light:
“Metallic” - looks like a shiny
metal (opaque, shiny,
metallic colors)
“Submetallic” - looks like a
duller metal
“Nonmetallic” - all others, e.g.,
glassy or vitreous, dull or
earthy, pearly, silky, waxy,
resinous, adamantine
Mineral Identification Properties
Pyrite
* Metallic
* Vitreous
* Resinous
©1995-2006 by Amethyst Galleries, Inc.
Quartz
* Greasy
* Pearly
* Silky
USGS
* Adamantine
Sphalerite
©2003, Alan Plante, Donald
Peck, & David Von Bargen
Mineral Identification Properties
* Metallic
Nepheline
and cancrinite
(yellow)
* Vitreous
Stellerite
* Resinous
* Greasy
* Pearly
* Silky
* Adamantine
Diamond
Gypsum
(variety satin spar)
all images ©2003, Alan Plante, Donald Peck, & David Von Bargen
Mineral Identification Properties
* Metallic
* Vitreous
* Resinous
* Greasy
* Pearly
* Silky
* Adamantine
* Earthy
* Dull
Limonite
StoneTrust Inc.
Mineral Identification Properties
* Metallic
* Vitreous
* Resinous
* Greasy
* Pearly
* Silky
* Adamantine
* Earthy
* Dull
Hematite
NOAA
Mineral Identification Properties
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Hardness
Crystal Form
Cleavage
Fracture
Color
Streak
Luster
Others
Striations - tiny, parallel
grooves on a cleavage
face. These form due to
crystal growth along
closely parallel surfaces
Norris W. Jones and Charles E. Jones © McGraw-Hill
Striations
Calcium Plagioclase
Feldspar
Mineral Identification Properties
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Hardness
Crystal Form
Cleavage
Fracture
Color
Streak
Luster
Others
Specific Gravity - “heftiness”
weight of volume of mineral
weight of same volume of water
Mineral Identification Properties
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Hardness
Crystal Form
Cleavage
Fracture
Color
Streak
Luster
Others
Tests only for Specific
Minerals:
- Taste
- Smell
- Magnetism
- Reaction to Acid
Mineral Identification Properties
Sulfur
smells like
rotten eggs
Halite
tastes like
salt
Grotzinger et al. © 2007 by
W.H. Freeman & Company
©1995-2006 by Amethyst Galleries, Inc.
Calcite
reacts with HCl
strongly
Dolomite
reacts with HCl
weakly
Magnetite
strongly
magnetic
© Lou Perloff / Photo Atlas of Minerals
© Lou Perloff / Photo Atlas of Minerals
© 2006 Robert James / YourGemologist.com
Objectives of Lab Exercise
• Define a mineral as an Earth material
• Define physical properties that
characterize minerals
• Use physical properties to identify
common rock-forming minerals
- this lab focuses on field tests (simple physical tests to
determine the mineral)
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