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Earth Materials: Minerals
What is a mineral?
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- solid
(excludes liquids and gases)
- crystalline
(three dimensional ordered arrangement of atoms
or molecules)
• What is a mineral?
- specific composition
(a single element or a compound that at least
comes close to a specific chemical formula)
• Importance and uses of minerals
- naturally-occurring
(not exclusively made by people on purpose)
• Describing and identifying minerals – Mineral properties
- single-phase
(made up of one kind of material; not a mixture –
i.e. to distinguish minerals from rocks)
• Why these properties? - Mineral structures, bonding, and composition
usually not of biological origin / inorganic (somewhat artificial distinction here)
• Major categories of minerals – Based on composition and structure
Examples to test:
• Ice (e.g. in snow or a glacier)
• Obsidian
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Minerals as Constituents of Rocks
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Importance of Minerals
• Almost all rocks are made of minerals!
• Aesthetic value
Minerals
in Granite
• Natural resource value
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Natural Resource Value
Aesthetic value
Native gold
A large cut diamond
Smithsonian
Smithsonian
Open pit copper mine south of Tucson, Arizona
Fig 22.22 Understanding Earth
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Mineral Properties
Importance of Minerals
• Natural resource value – Our society can’t function without minerals!
Three general categories:
Optical
Physical
Mineral Information Institute http://mii.org/
- Lifetime consumption http://mii.org/pdfs/baby.pdf
- Per-capita minerals use http://mii.org/pdfs/percapita.pdf
- Importance of mining http://mii.org/pdfs/MiningImportance.pdf
- Fact sheets, etc.
Chemical
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Mineral Properties
Some optical properties
Minerals of various colors
Color
Understanding Earth
Streak
Luster
Double refraction
Fluorescence
Transmission of light (transparent, translucent, or opaque)
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Streak
Example: hematite
Metallic luster:
gold and pyrite
Fig 2.26 Understanding Earth
Non-metallic luster:
feldspar, mica, olivine, and
quartz
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Double refraction in a transparent piece of calcite
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Mineral Properties
Some physical properties
Hardness
Density
Crystal shape
How it breaks: cleavage and fracture
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Crystal of galena (left) (lead sulfide)
Crystal of quartz (right) (silicon dioxide)
These minerals differ in color, luster, light transmission, crystal form,
hardness, cleavage, and streak.
Understanding Earth
Fig 2.10 Understanding Earth
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Mineral Properties
How a mineral breaks:
Fracture
Cleavage
- key observations for cleavage:
- number of directions
- angles between them
Conchoidal
fracture in obsidian
Fig 4.3 Understanding Earth
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Cleavage in calcite
Fig 2.24 Understanding Earth
Cleavage of mica
into thin sheets
Fig 2.23 Understanding Earth
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Mineral Properties
Mineral Properties
Chemical properties
Acid test
Salty taste
Many other chemical tests
Some other properties
Habit
M
Magnetism
ti
Absorbs water
Smell
Fig 2.22 Understanding Earth
barite rosettes
(barium sulfate)
needles of stibnite
(antimony sulfide)
Some
unusual
crystal
Habits
Geology 2nd ed.
ed
Chernicoff
botryoidal
malachite
(green) with
azurite (blue)
(hydrous copper
carbonates)
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In-class exercise
Working in groups,
examine and describe the properties of each
mineral sample provided
stellate pyrite
(iron sulfide)
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Mineral Properties
Chemical bonds - how multiple atoms are held together
Mineral Properties
ionic
Relationship to:
atomic composition
covalent
l t
atomic structure and bonding
metallic
other types of bonding
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Carbon atom
Fig 2.2 Understanding Earth
Graphite and Diamond
Both are composed of carbon
but have very different
properties. Fig 2.15 Understanding Earth
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Structure
of halite
(sodium
chloride salt)
Fig 2.16
Understanding Earth
Structures of
graphite (left) and
diamond (right)
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Geology 2nd ed. - Chernicoff
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Ionic bonds hold
together Cl -1 and Na +1
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Understanding Earth
Regular arrangement of
atoms in galena (left)
Cube-shaped crystals
(below)
The structure of galena is essentially
the same as in halite. Therefore, both
grow and break to form cubes. Their
color and luster are different,
however, because they have different
compositions (and bonding).
Fig 2.10 Understanding Earth
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Some major groups of minerals
Silicates
e.g. quartz, feldspar, mica, olivine
(categorized by type of structure)
Non-silicates:
Carbonates
Oxides
Sulfides
Sulfates
Native elements
Halides
e.g. calcite
e.g. magnetite, hematite
e.g. pyrite, galena
e.g. gypsum
e.g. native gold, copper
e.g. halite
Silicon-oxygen tetrahedron
Fig 2.16 Understanding Earth
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Some Online Resources
Mineral resources info. from the USGS
http://minerals.er.usgs.gov/minerals/
http://minerals.er.usgs.gov/
http://www.usgs.gov/science/science.php?term=745
WebMineral Minerals Database
http://www.webmineral.com/
individual
tetrahedra
single
i l
chains
Types of silicate
mineral structures
Figs 2.17 and 2.18 Understanding Earth
double
chains
3-D
frameworks
sheets
MinDat Minerals Database
http://
http://www.mindat.org/
mindat org/
Smithsonian Gem & Mineral Collection
http://www.gimizu.de/sgmcol/
Smithsonian Department of Mineral Sciences
http://www.minerals.si.edu/
More rock and mineral links (some with lesson plans)
http://edtech.kennesaw.edu/web/rocks.html
http://www.dlese.org/dds/browse_su_0k.htm (Digital Library for Earth System Education)
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