Lecture 9 Synopsis:
Primary Silicate Minerals
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The earth's crust (and soils) are dominated by
8 elements, and the chemical arrangement of the 3 most abundant drives the
mineralogical structure of the earth. The earth is dominated by silicates
minerals (or including Al, aluminosilicate minerals),
which are covalent-like bonds between Si and
O, and Al and O. The linkages of the silica tetrahedron (
Si, 4O), determines the classification of the silicates - and their
behavior in soils. Increasing
complexity of tetrahedral linkages, combined with decreased abundance of
cations held by ionic bonds, corresponds
to increasing stability of the minerals in soil environments. In summary,
the characteristics that affect the stability of silicates to weathering
are: 1. complexity of tetrahedral linkages 2. presence of Fe+2 3. substitution of
Al+3 for Si+4 To appreciate mineral structure, we have assembled two options for viewing their characteristics. The first is the web site (minerals and molecules) and the second are the minerals structures that are attached. These were derived from the software "Atoms". |