No abstract

No abstract

No abstract

Combined visual cathodoluminescence (CL) and spectral analyses of CL reveals periodic enrichments of rare earth elements (REE3+) and manganese (Mn2+) within the laminations of eight calcitic lateglacial to postglacial stalagmites. In the annual layers, the enrichment of trace elements can be correlated with the autumn/winter laminae, which are strongly pigmented and rich in organic carbon. During the Holocene, they occur especially in the Atlantic stage and in subrecent/recent times. The enrichment of REE3+ and Mn + reflects times of more intense weathering, which presumably prevailed during the Atlantic warm and humid climate. In subrecent/recent times, especially the last 100 years, these enrichments may have been at least partially anthropogenically induced.

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.

No abstract

Five smithsonite samples from locations in Germany, Mexico and Namibia have been investigated with cathodoluminescence (CL) spectroscopy and trace-element analyses. As with other carbonates, the CL properties of smithsonite are mainly controlled by Mn 2+ -and Fe 2+ -incorporation, because these elements are the most important activator and quencher species, respectively. Additional trace elements may have either a quenching effect (Cu) or have only small or no influence (Ca, Pb). A linear correlation exists between the Mn content and the intensity of the Mn-emission band in smithsonite, which can be quantified, if the Cl intensity is related to the number of moles of Mn rather than the weight fraction. A correlation between the Cl intensity and the Mn concentration, which is valid for all trigonal carbonates, is obtained from the published results of calcite, dolomite and smithsonite. Matrix effects due to the different chemical composition of the carbonate minerals seem to be of lesser importance.

The cathodoluminescence analyses of the trigonal carbonates calcite and dolomite have been applied intensively in sedimentary petrology for a long time and the properties of these minerals are well-known, but much less attention has been paid to aragonite. In this study, the cathodoluminescence behaviour and the trace element composition of natural and synthetic aragonite have been studied employing trace element analyses (proton induced X-ray emission) and luminescence spectroscopy. Aragonite doped with Mn 2+ has been synthesized in a NH 4 + -Mg 2+ -Ca 2+ -Cl ) solution in contact with a CO 2 -H 2 O-NH 3 atmosphere. The low effective distribution coefficients indicate a rapid growth of the crystals of millimetre size which occurred within hours or days. The natural aragonite samples contain Mn, Fe and Sr in different concentrations. The Mn-bearing aragonites exhibit a bright green luminescence which is caused by a strong emission band at 575 nm with a half-width of about 84 nm. The luminescence intensity shows a strong positive correlation with Mn in aragonite when Fe and Mn do not exceed 2000 p.p.m. The intensity is depressed if the concentration of these elements exceeds the critical values. In the shell of a recent Unio sp., the luminescence intensity deviates from the linear correlation, although the trace element contents are not too high; this is probably an effect of quenching by organic material between the crystallites of the biogenic aragonite.