A photoelectron spectroscopy study of lava stones

Abstract

In areas surrounding volcanoes, atmospheric agents remove surface layers from the emitted stones that go directly into the air and groundwater. The chemical composition of magmatic stones is currently studied using techniques that do not differentiate between bulk and surface composition. To the best of our knowledge there are no XPS investigations of magmatic stones. Therefore, in this study we report on the first surface chemical investigation of magmatic stones, and in particular of lapilli emitted by the Etna volcano (Sicily), using the X-ray photoelectron spectroscopy technique. Results show important differences between bulk and surface composition of major oxides. We found that Si, Fe, Ca and K segregate into the bulk, whereas Al, Na, P and Mn segregate on the surface. For example, the Mn surface concentration is 266.7% with respect to that observed in the bulk, and is due to the water soluble MnOOH species at the surface. The present study highlights the potentiality of the XPS technique in the investigation of the surface composition of magmatic materials.