Journal
CRYSTALS
Volume 11, Issue 2, Pages -Publisher
MDPI
DOI: 10.3390/cryst11020109
Keywords
willhendersonite; chabazite; zeolites; Lessini Mounts
Funding
- Department of Pure and Applied Sciences of the University of Urbino Carlo Bo
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Willhendersonite is a rare zeolite with limited occurrences globally, and this study reports a new occurrence from the Tertiary volcanic rocks in the Lessini Mounts, northern Italy. The morphology, mineralogy, and chemical composition of the crystals show significant variability, from Ca-rich to Ca-K compositions, highlighting the existence of an isomorphous series.
Willhendersonite is a rare zeolite, with very few occurrences reported globally (Terni Province, Italy; the Eifel Region, Germany; Styria, Austria). Moreover, the data available from these sites are very limited and do not allow a detailed picture of this zeolite's mineralogical and chemical characteristics. In this work, a new willhendersonite occurrence is reported from the Tertiary volcanic rocks of the Lessini Mounts, northern Italy. Morphology, mineralogy and chemical composition of selected crystals were studied by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray Diffraction (XRD), and electron probe microanalyser (EPMA). Willhendersonite occurs within basanitic rocks as isolated, colorless, transparent crystals with prismatic to flattened morphologies. Individual crystals often grow together to form small elongated clusters and trellis-like aggregates. The diffraction pattern exhibits 33 well-resolved diffraction peaks, all of which can be indexed to a triclinic cell with unit cell parameters a = 9.239(2) angstrom; b = 9.221(2) angstrom; and c = 9.496(2) angstrom, alpha = 92.324(2)degrees, beta = 92.677(2)degrees, gamma = 89.992 degrees (Space Group P (1) over bar). The chemical data point to significant variability from Ca-rich willhendersonite (K0.23Na0.03)(Sigma=0,26)Ca-1.24 (Si3.06Al3,00Fe0.013+)(Sigma=6,07) O-12 center dot 5H(2)O) to Ca-K terms (K0.94Na0.01)(Sigma=0,95)Ca-0.99 (Si3.07Al2.93Fe0.003+)(Sigma=6,00)O-12 center dot 5H(2)O). Willhendersonite from the Lessini Mounts highlights the existence of an isomorphous series between the Ca-pure crystals and Ca-K compositions, possibly extended up to a potassic end-member.
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