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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• 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 low-temperature 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