Minerals

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Minerals
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• The earth is made of rocks, which are in turn
  made of minerals. In this part of the course
  we'll learn how to identify common minerals and
  rocks.
• In order for something to be classified as a
  mineral, it must meet five (5) criterion
• Minerals are
•         1. Naturally occurring,
•         2. Inorganic,
•         3. Have known chemical compositions
•         4. Have definite physical properties.
• 5. Are solid
•        
• They are usually (although not always)
  crystalline.

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•  Mineral Classification
• Minerals are classified based on chemical
  composition and crystal structure.
• Minerals are made of different ions bonded
  together.
• Ions are charged atoms
•         Cations are positively charged whereas
•         Anions are negatively charged
•  
• Common ions in earth's crust
• O - most common ion (anion)
• Si, Al, Fe, Ca, Na, K, Mg, (Cations)
• Minerals are made mainly of these ions
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• Crystal structure
• Crystal structure depends on sizes of and charges
  on ions

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• Crystal structure
• Crystal structure depends on sizes of and charges
  on ions
•  
• Most common mineral group is the silicates
• All silicate minerals contain silicon and oxygen
• 1. Mafic silicate minerals contain iron or
  magnesium and are dark in color.
• Examples olivine, pyroxene, amphibole, and
  biotite mica
• 2. Felsic silicates don't contain magnesium or
  iron, and are light in color.
• Examples feldspar, quartz, clay minerals,
  muscovite mica

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Mafic silicate
Felsic silicate
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• Silicate mineral structures
• Basic building block silica tetrahedron
• Silica tetrahedron is a silicon ion bonded to 4
  oxygen ions
• Silicon is positively charged (4)
• Oxygen is negatively charged (-2)
• Net charge on tetrahedron -4
• Because entire tetrahedron is negatively charged,
  it is attracted to cations
• Tetrahedra may link together by a cation (e.g.
  Mg, Fe, Na, Ca, K) serving as a bridge, or may
  link together by sharing oxygens
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Silica Tetrahedron
Silicon
Oxygens
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• Isolated tetrahedral structure
• Cations serve as links between tetrahedra no
  sharing of oxygens
• e.g. olivine, and garnet, which also happen to be
  mafic silicates
•  
• Single chain silicates
• Adjacent tetrahedra form a chain by sharing 2 of
  their oxygens with neighboring tetrahedra
• e.g. pyroxenes, which also happen to be mafic
  silicates
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• Double chain silicates
• Two chains can link up by sharing oxygens
• e.g. amphiboles, which are mafic silicates too
•  
• Sheet silicates
• Sheets are formed when each tetrahedron shares 3
  of its oxygens with its neighbors
• e.g. micas, biotite (mafic) and muscovite
  (non-mafic), and clay minerals, which are
  non-mafic silicates
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• Framework silicates
• Every oxygen in each tetrahedron is shared to
  form 3-D framework
• e.g. feldspar, quartz, which are also non-mafic

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• Common non-silicate minerals
• Fluorite used as a toothpaste additive
• Calcite -- calcium carbonate -- Limestone is made
  of calcite.
• Dolomite -- calcium magnesium carbonate
• Gypsum -- calcium sulfate
• Galena -- lead sulfide
• Pyrite -- iron sulfide
• Halite -- sodium chloride (table salt)

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• How to Identify Minerals Physical Properties
• Geologists determine the identity of an unknown
  mineral by describing its physical properties.
  They then use a reference book to find out what
  mineral has those properties. We will learn to
  describe the physical properties.
•  
• 1. Habit refers to the overall shape of the
  mineral. Scientists use terms like "equant" (3
  dimensions of the mineral have about the same
  length, like a cube or sphere), elongate" (one
  direction is long but the other 2 are short, like
  a pencil), or "platy" (one dimension is short,
  other 2 are long like a sheet of paper)
• Isolated tetrahedra framework silicate
  minerals tend to be equant in habit chain
  silicates tend to be elongate, sheet silicates
  are platy
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• 2. Luster refers to the light reflected off of
  the mineral and its overall quality. Minerals
  can be termed glassy, opaque, transparent,
  shiny, or most commonly metallic and
  non-metallic.
• One of the first determinations a geologist
  must make is whether the mineral in metallic or
  non-metallic.

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Non-metallic mineral
Metallic mineral
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• Cleavage
• Refers to very smooth, flat, shiny breakage
  surfaces
• These special breakage surfaces correspond to
  zones of weak bonding in the crystal structure.
• To describe cleavage, one must determine the
  number of unique cleavage planes (directions) and
  their angle with respect to each other (e.g. salt
  breaks into cubes, with cleavage in 3 directions,
  all at 90 degrees)
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NO cleavage
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• Hardness
• Refers to "scratchability" or resistance to being
  scratched. Harder minerals will scratch softer
  minerals.
• Geologists rank minerals according to hardness
  using the Moh's scale
• Moh's Hardness Scale (Commit this to memory)
• 1.0     TALC
• 2.0    GYPSUM
• 2.5 FINGERNAIL
• 3.0    CALCITE
• 3.5    COPPER PENNY
• 4.0    FLUORITE (Note the spelling!)
• 5.0    APATITE
• 5.5    STEEL KNIFE BLADE/GLASS PLATE
• 6.0    ORTHOCLASE FELDSPAR
• 7.0    QUARTZ
• 8.0     TOPAZ
• 9.0     CORUNDUM (RUBY)
• 10.0 DIAMOND

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• Color
• Varies in many minerals, e.g. quartz
• VERY unreliable.
• Some minerals come in just one color
• other are many colors/many varieties.
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• Streak
• Refers to color of mark left by rubbing mineral
  against a streak plate (unglazed porcelain).
  Streak does not vary even if color does.
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• Other Properties
• Some minerals are magnetic (i.e., magnetite)
• Some minerals effervesce ("fizz") in dilute acid
  (calcite)
• Specific gravity (like density) galena has a high
  specific gravity.

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Key Terminology

• Mineral Chemical composition
• Crystalline structure Ions
• Cation Anion
• Silicate Mafic
• Felsic Silica tetrahedron
• Single chain Double chain
• Sheet silicate Framework silicate
• Non-silicate Physical properties
• Habit Luster
• Streak Cleavage
• Hardness Mohs Hardness Scale

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Pertinent Web Sites

• Amateur Mineralogy Links
• A very extensive listing of links to sites
  related to mineralogy.
• Ask a Geologist
• If you have questions, a professional geologist
  is here to help.
• Ecole des Mines de Paris Mineralogy
• Here are some beautiful mineral pictures from a
  museum in Paris.
• Gems and Precious Stones
• Jill Banfield's (University of Wisconsin-Madison)
  integrated body of information about gems and
  gemstones.
• Gold Institute
• A good commercial site with a lot of information
  about gold.
• Gold Prospecting
• A good source for information about recreational
  gold prospecting.
• Mineral and Gemstone Kingdom
• This site contains a comprehensive list of
  minerals and their properties.
• Mineral and Rock Description (National Park
  Service)
• Mineral and rock photographs and descriptions
  from the National Park Service.
• Mineral Data Links
• Links to several mineralogy related Web sites.
• Mineral Descriptions and Images

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Minerals Links (NAGT) An extensive listing of
mineral links arranged by topic from the National
Association of Geology Teachers (NAGT). Minerals
Links (University of Würzburg) An extensive
listing of mineral links including mineral
descriptions and thin section images. Minerals
(Mineralogical Society of America) The
Mineralogical Society of America web site offers
a good, general description of mineral
properties, classification, etc. directed
primarily toward K-12 grade students. Minerals
(Trinity Mineral Company) Beautiful photos of
rare minerals offered for sale by the Trinity
Mineral Company. Minerals Information (USGS)
United States Geologic Survey (USGS) statistics
and information on the worldwide supply, demand,
and flow of minerals and materials essential to
the U.S. economy, the national security, and
protection of the environment. Minerals on the
Internet A wide variety of minerals-related
sites sorted into relevant categories from Tasa
Graphic Arts, Inc. Mining and Mineral Resources
A great source for information about mining of
mineral resources, mining news and trends,
etc. National Mining Association The National
Mining Association (NMA) represents the mining
industry, mining equipment manufacturers, and
other mining-related businesses, throughout the
United States. Periodic Table of the Elements
In addition to listing a wealth of information
about each element, this location also lists and
describes numerous compounds.
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Periodic Table of the Elements II A great source
for information on the elements. Resource Fact
Sheets (USGS) United States Geological survey
(USGS) activities in the natural resources theme
area inventory the occurrence and assess the
quantity and quality of natural resources.
Activities also include monitoring changes to
natural resources, understanding the processes
that form and affect them, and forecasting the
changes that may be expected in the
future. Resources from Space University of
Wisconsin course notes with links to several
essays about resources from space. Resource
Sustainability An essay that examines the future
of Earth's resources. Rock and Mineral
Collecting (USGS) Selected references on rocks,
minerals, and gemstones from the United States
Geological Survey (USGS). Rockhounds Information
Page The Rockhounds Information Page offers many
links to mineral and rock related
Websites. Smithsonian Gem Mineral Collection
Images of mineral and gemstone specimens found
in the Smithsonian Institution. (Not an official
Smithsonian site) Society for Mining, Metallurgy
and Exploration, Inc. The Society for Mining,
Metallurgy, and Exploration (SME) is an
international society of professionals in the
minerals industry. Society of Economic
Geologists The Society of Economic Geologists,
Inc. (SEG) is an international organization of
individual members with interests in the field of
economic geology. State Minerals Information
(USGS) Statistics and information on the supply,
demand, and flow of minerals and materials
essential to the U.S. economy, the national
security, and protection of the environment from
the United States Geological Survey (USGS).
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Technical University of Clausthal This site at a
German university also shows some excellent
mineral pictures. Virtual Atlas of Opaque and
Ore Minerals This site provides over 400 full
colour photomicrographs of the major ore-forming
associations and opaque minerals in
non-mineralized rocks. It describes typical
examples of each material from many classical
localities throughout the world. For each
association there is a listing of the major (and
important minor) primary ore minerals, alteration
products and gangue, typical textures, a brief
discussion of the geology of the association and
a list of references. World Lecture Hall
(University of Texas at Austin) The World
Lecture Hall features links to online courses in
the United States and Canada. Simplest to use
for Mineral I.D. Lab Virtual Rock Bag
http//comp.uark.edu/sboss/vrockbag.htmminerals