Transcript Introduction to Environmental Geochemistry

Oxides and Hydroxides
GLY 4200
Lab 3 - Fall, 2012
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Oxides
• Oxygen is by far the most abundant element
in the earth’s crust
• > 60% by atomic proportion
• Many minerals contain oxygen
• Only those minerals where the oxygen is
combined with metallic elements directly
are oxides
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Anionic Groups Containing Oxygen
• Almost all non-metallic elements form
structural groups with oxygen, and then
these groups combine with the metallic
elements
 Examples:
• Carbonates CO3
• Phosphates PO4
• Tungstates WO4
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Oxide Classification
• Oxides can be divided into classes
 Simple oxides, which contain one cation type in
association with oxygen
 Multiple oxides, which contain more than one
cation type in association with oxygen
 Hydroxides are minerals which contain the
OH-1 group, the oxygen’s are directly bound to
the metal with a single bond
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Simple Oxides
• Possible types: XO, X2O, XO2, X2O3
 X is a metal cation
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Multiple Oxides
• Possible types: XY2O4, and XY2O6
 X and Y are metal cations
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Oxide Group Properties
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•
•
•
Dense
Relatively hard
Refractory (melt at a high temperature)
Occurance:
 Often found as accessory minerals in igneous
and metamorphic rocks
 Because of their hardness, as resistant grains
and detrital grains in sediments and
sedimentary rocks
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Hydroxide Group Properties
• Usually soft to moderate hardness
• Lower densities than oxides
• Occurance: alteration products formed by
weathering, hydroxides are necessarily lowtemperature minerals
• High temperatures would cause dehydration
and would destroy the crystal structure
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Ore Minerals
• It is harder to obtain metals from oxides
than from sulfides, because metal-oxygen
bonds are stronger
• Some elements prefer to bond to oxygen,
and do not occur as sulfides, so the ores are
oxides
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Oxide Ores
Mineral
Element or Gem
Cuprite
Copper
Corundum
Rubies, Sapphires
Hematite, magnetite
Iron
Ilmenite
Titanium
Purolusite
Manganese
Cassiterite
Tin
Uraninite
Uranium
Chromite
Chromium
Columbite-Tantalite
Niobium, tantalum
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Hydroxide Ore
• Bauxite is the major ore of aluminum
• It is a rock name, not a mineral name
 Mixture of diaspore, gibbsite, and boehmite
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Text Reference
• See chapter 16 in the text for more
information on oxides and hydroxides, pp.
368-393
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