1 Oxides and Hydroxides GLY 4200 Lab 3 - Fall, 2012

2 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

3 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 CO 3 Phosphates PO 4 Tungstates WO 4

4 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

5 Simple Oxides Possible types: XO, X 2 O, XO 2, X 2 O 3  X is a metal cation

6 Multiple Oxides Possible types: XY 2 O 4, and XY 2 O 6  X and Y are metal cations

7 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

8 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

9 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

10 Oxide Ores MineralElement or Gem CupriteCopper CorundumRubies, Sapphires Hematite, magnetiteIron IlmeniteTitanium PurolusiteManganese CassiteriteTin UraniniteUranium ChromiteChromium Columbite-TantaliteNiobium, tantalum

11 Hydroxide Ore Bauxite is the major ore of aluminum It is a rock name, not a mineral name  Mixture of diaspore, gibbsite, and boehmite

12 Text Reference See chapter 16 in the text for more information on oxides and hydroxides, pp