Composition of the Earth’s Crust Our planet’s crust is mostly silica.

Silica Tetrahedron

Silica Tetrahedral Framework 3-D framework Each silica tetrahedron is joined to its 4 nearest neighbours by sharing the oxygens at the vertices of the tetrahedra. Each oxygen is bonded to two silicons, and each silicon is bonded to 4 oxygens. The overall ratio is: SiO2 The molecule extends out in all directions. Each crystal is a single marcomolecule.

Tectosilicates: Framework Silicates Silica SiO2

Alpha Beta Quartz (12%)

2D view of the 3D framework in silica glass. (modern glass has other components in it)

Feldspars Silica framework molecules in which a set ratio of silicon atoms are substituted with aluminum atoms. Since aluminum has one fewer electrons than silicon, an additional metal atom must be squeezed into the gaps between the tetrahedra to provide the additional electron. The mineral still forms a macromolecular lattice, just slightly more complex. The distortion in the lattice structure caused by the other metal ions produces the cleavage planes of weakness.

Orthoclase Feldspar (12%) KAlSi3O8 1 aluminum tetrahedron for each 3 silica tetrahedra: So, could be written as: K(AlO2)(SiO2)3

Plagioclase Feldspars (39%) Solid Solution from: NaAlSi3O8 to CaAl2Si2O8 Also could be: Na(AlO2)(SiO2)3 and Ca(AlO2)2(SiO2)2

Phyllosilicates: Sheet Silicate micas (5%) and clay minerals (5%) Kaolinite Muscovite

Inosilicates: Single Chain Silicates Pyroxenes (11%) There are two tetrahedra in the unit cell. Two oxygens are shared outside of the cell and 1 is shared within. Thus, there are 4 oxygens not shared, so the charge is 4-.

Inosilicates: Double Chain Silicates Amphiboles (5%) There are 4 tetrahedra in the unit cell. 4 oxygens are shared with other cells and 3 are shared within the cell. This leaves 6 unshared oxygens, thus the 6- charge.

Nesosilicates: Island Silicates Isolated Silica Tetrahedra Olivines (<3%)

Garnet X3Y2(SiO4)3 X = 2+ ions: Ca, Mg, Fe, Mn Y = 3+ ions: Al, Fe, Cr

Non-Silicate Mineral Groups (<8% of the crust in total) Carbonates Sulfates Halides Oxides Phosphates Sulfides Hydroxides Elements

Carbonates Flat, rather than tetrahedral. Forms ionic substances rather than polymerizing to make macromolecules. Can be produced by both inorganic and organic processes.

Calcium Carbonate

Calcite

Dolomite MgCa(CO3)2 Distinguished from calcite and aragonite by visibly reacting with 10% HCl only when powdered.

Siderite FeCO3 Rhodochrosite MnCO3 Azurite Cu3(CO3)2(OH)2 Malachite Cu2CO3(OH)2

Usually the first mineral to start precipitating when sea water evaporates.

Halides Halite NaCl Fluorite CaF2

<-- hematite with powdery surface Oxides Hematite Magnetite Fe2O3 Fe3O4 (FeO + Fe2O3) Corundum Al2O3 Includes sapphire and ruby <-- hematite with powdery surface

Phosphates Apatite Ca10(PO4)6(OH,F,Cl)2 Sulfides Pyrite FeS2 Galena PbS

Hydroxides Gibbsite Al(OH)3