Geoscience Reference
In-Depth Information
13
The element barn
This chapter is intended to provide a geochemical overview of a number of important ele-
ments. The elements will be grouped according to mixed criteria, in particular their position
in the periodic table and their geochemical properties. We will describe the major mineral
phases that host these elements in the mantle and the crust, their properties in solution, and
the processes by which they are transferred from any major reservoir (mantle, crust, ocean)
to its neighbors. We will not reproduce here the terrestrial abundances, which can be found
in Appendix A . We will nevertheless provide the reader with some important data. Conden-
sation temperatures in the solar nebula (Wasson, 1985 ; Lodders, 2003 ) define the volatile
versus refractory character of the element. The solubility and complexation data in surface
waters (Morel and Hering, 1993 ) and the residence times in seawater (Broecker and Peng,
1982 ) constrain the concentration level and speciation in natural waters at low temperature.
Different parts of geochemical cycles may receive uneven attention. This inhomogeneous
treatment reflects the power of geochemistry: different elements are used to trace different
processes. The atmophile elements, which essentially fractionate in to the atmosphere and
the ocean are not considered in this chapter (N, O, H), while only the long-term aspects of
the carbon cycle have been addressed.
13.1 Silicon
Most common form: Si 4 +
Ionic radius: 0.26 Å
Stable isotopes: 28 (92.23%), 29 (4.67%), 30 (3.10%)
Atomic weight: 28.086
Condensation temperature: 1311 K
 
 
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