Environmental Chemistry

Chart 4.1
main types of primary minerals in soil
Primary minerals Properties
silicates
oxides
sulphides
phosphates
Including minerals such as feldspar (e.g. KalSi 3 O 8 ), mica
(e.g. K(Si 3 Al)Al 2 O 10 (OH) 2 ), pyroxene (e.g. (Mg,
Fe) 7 (Si 4 O 11 ) 2 (OH) 2 ) and olivine (e.g. (Mg, Fe) 2 SiO 4 ), most of
which are unstable, easy to be weathered and to release
elements such as sodium, potassium, calcium, magnesium
and iron, etc. that are aborpt by plants and form new
secondary minerals.
Including rutile (TiO 2 ), quarts (SiO 2 ), hematite (Fe 2 O 3 ) which
are highly stable, difficult to be weathered and contribute
little to nutrition for plants.
Mainly in the forms of alkaline compounds, ad. pyrite and
marcasite. These two minerals are isomeric, easy to be
weathered and the main source of sulphur element in soil.
Phosphorite is the most widespread phosphate mineral in
soil, including flurapatite (Ca5(PO4)3F) and (Ca5(PO4)3Cl),
followed by iron phosphates, aluminum phosphates and
other phosphates. It is the main source of phosphorus in
soil.