Authigenic quartz overgrowths and hydrothermal quartz crystals from locations
in Oman and Switzerland have been investigated with SIMS, EPMA, SEM-CL and SEM-CC.
All techniques reveal similar zonation patterns with SEM-CL having the best
resolution followed by SEM-CC, EPMA and finally SIMS. The observed zonations
reflect chemical and/or physical changes during growth in the precipitation
environment or disequilibrium precipitation at the crystal surface (i.e. sectoral
and intrasectoral zonation). Based on the total Al content, two types of
authigenic quartz are distinguishable. When the Al concentration is <500 μg
g–1 the predominant CL emission is at ~630 nm; in such
quartzes, SEM-CL and SEM-CC are directly correlated, and signal intensities drop
as a function of increasing Al concentration. In contrast, authigenic quartz with
Al concentrations between 500 μg g–1 and 1000 μg
g–1 has CL emission maxima at both ~630 nm and ~380—400
nm, at which point the panchromatic SEM-CL and SEM-CC intensities become
decoupled.
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