The minor and trace elements present in minerals have long been regarded as retaining important clues to the crystallization and post-crystallization histories of rocks and minerals. Countless studies have examined the presence and concentrations of specific elements as fingerprints of various petrogenetic environments or processes, and their utility is evident in fields as diverse as igneous crystallization and porosity occlusion in shallow aquifers. Whereas many of the factors controlling the distribution of trace elements are well known, there has recently been much attention given to the role of mineral surfaces in influencing element incorporation during crystal growth. Examples of the influence of mineral surfaces on element incorporation are in fact well known to mineralogists in the form of sectoral zoning in such common minerals as augite, staurolite, quartz, calcite, topaz, and zircon (e.g., Hollister, 1970; Dowty, 1976; Reeder and Paquette, 1989; Vavra, 1990). Sectoral zoning arises from differences in the incorporation of minor elements at symmetrically nonequivalent crystal faces during growth, expressed as compositionally distinct growth sectors (Figure 6.1). Reeder (1991) has emphasized the fundamental geometrical and temporal differences of this zoning type in relation to the more common concentric growth zoning; in the familiar case of concentric zoning the surface across which composition changes coincides with prior growth surfaces and hence the zoning pattern records temporal variations in element incorporation. In the case of sectoral zoning, however, the interface across which composition changes cuts across prior growth surfaces and coincides with sector boundaries.
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- Surface Structural Controls on Trace Element Incorporation during Crystal Growth
Richard J. Reeder
- Springer Netherlands
- Chapter 6