The hydrous component in leucite from Somma-vesuvius and Roccamonfina volcanoes (southern Italy) -a FTIR spectroscopic Investigation

摘要

FTIR microspectroscopic data on the hydrous species occurring in leucites from different host rocks of Somma-Vesu-vius and Roccamonfina volcanoes (southern Italy) are reported. All leucite samples contain significant amounts of structurally in-corpored H_2O molecules, confirmed by the H_2O combination band at 5226 cm~(-1). Three main types of infrared spectra can be discerned. Type 1, with a single band maximum at 3600 cm~(-1) represents the typical spectrum of the Somma-Vesuvius samples, whereas type 2, revealing two additional band maxima at 3654 and 3506 cm~(-1), characterises the Roccamonfina crystals. Type 3, showing a broad absorption band with a band maximum around 3390 cm~(-1) was encountered only in two Vesuvian samples. Due to the presence of three discernible band maxima and of four to five deconvoluted component bands, the presence of at least two different H_2O molecules can be derived. Estimates of the water content give values between 40 and 2777 wt.ppm for the Somma-Vesuvius samples; a zoning of the water content is inherent to the Vesuvian leucite crystals. Roccamonfina leucites show significantly higher and very homogeneous water contents in the range of 4602 to 5700 wt. ppm, suggesting the influence of an environmental factor on the growth of the crystals.