Classification

The characterization of different pumices follows a three-step
procedure consisting of:
• Microscopical investigation to check the mineral assemblage
• Homogenization of a suitable, representative quantity
• INAA
Comparison of the concentrations of some characteristic elements can lead to clear identifcation in some cases .

Figure 12, Ta versus Eu

The juxtaposition of relative concentrations yields further important information to differentiate products from different volcanic sources, e.g. the distinction of pumices from Giali and Nisyros.

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Figure 13, Eu/Ta versus Th/Hf

It is even possible to distinguish the chemically highly similar products of the Lower Pumice sequence (Bu1 and 2) and the Upper Pumice („Minoan“ pumice, Bo) of Santorini.

Figure 14, Eu/Th versus Ba/Ta

< Figure 15, Eu/Ta versus Th/Hf

Normalization of element concentrations to the Upper Pumice of Santorini (Bo) has been found to be the most efficient way of comparing all information gathered. Normalized data stay within a range of two orders of magnitude and can thus be plotted with highest resolution. More widely used normalizations (continental crust, chondrite) can hardly resolve the small variations in the trace element concentrations. Due to the small data sets and the lack of consideration of the geochemical background and chemical properties, statistical methods like cluster analysis are not applicable.