Mineralogy and speleogenesis of the Corona ‘e sa Craba quartzite cave (southwest Sardinia).

Sa Corona ‘e sa Craba (Barbusi, Carbonia, Southwest Sardinia) is a natural cave almost entirely developed within a quartzite vein. Its natural entrance, enlarged during mining operations, opens at 260 m asl. The cave is composed of an over 200 m long and 20 m wide gallery developed in a NW-SE direction. During our surveys we collected over 50 small samples of crusts, coatings and spars from all over the cave, on which we performed X-ray diffraction analysis in order to understand the speleogenetic pathways. These samples ranged in color from yellow to red, purple, brownish, grey, white, pinkish, bluish and black. Beside the already known minerals, the following have been discovered for the first time within this cavity: sulfide: cinnabar; sulfates: alunite, natroalunite, basaluminite, walthierite and gypsum; phosphates: taranakite, spheniscidite, robertsite, Al-rich strengite, hydroxylapatite, vashegyite and an unnamed Pb-Mo oxide phosphate; silicates: halloysite, lizardite and clay minerals of the illite and smectite group; oxyhydroxides: hematite, goethite, pyrolusite and todorokite