Punta del Coltellazzo, the eastwarding subpromontory of Capo di Pula on which the Sant'Efiso tower (also known as Torre del Coltellazzo) is located, is made of andesitic lava with porphyric texture, pyroclastites and grey conglomerates of andesitic lava clasts. The conglomerates are locally fractured and crossed by veins containing zeolites, calcite, and quartz. Small outcrops of these zeolite-bearing conglomerates embedded in andesitic lava are found in the steep cliffs above the sea along the north, east, and south coasts of Punta del Coltellazzo, below Sant'Efisio tower. From two different outcrops, located just a few dozen metres away from each other along the south coast, the type specimens of barrerite and stilbite-Na have been collected.

Barrerite (Passaglia & Pongiluppi, 1975; Galli & Alberti, 1975) was originally described as sodian stellerite (Passaglia & Pongiluppi, 1974; Pongiluppi et al., 1974; De Michele, 1974; Boscardin, 1975). The type material appears as white or slightly pinkish tabular crystals filling the rock fractures, associated with reddish incrustations of Sr- and Ba-bearing heulandite-Ca (CaO 4.66 wt%; Na2O 1.80 wt%; K2O 0.89 wt%; SrO 0.81 wt%; BaO 0.53 wt%; Fe2O3 0.40 wt%; MgO 0.38 wt%).

Stilbite-Na (Coombs et al., 1997) was originally described as high-sodium stilbite (Pongiluppi, 1974; Passaglia et al., 1978; Quartieri & Vezzalini, 1987). The type material, which appears as white fasciculated crystals and for which sodium is the dominant extra-framework cation (Na2O 4.83 wt%; CaO 2.07 wt%; K2O 0.90 wt%; MgO 0.16 wt%; SrO 0.03 wt%), was collected from large veins cropping out in the cliff beyond Sant'Efisio tower, a few dozen metres away from the barrerite site and at a higher level.

NOTE: Since the area is situated in the Nora archaeological excavation site, collecting is strictly prohibited.

Other Regions, Features and Areas containing this locality

References