Guano-derived morphologies and associated minerals found in Cova de sa Guitarreta, Llucmajor, Balearics

Cova de sa Guitarreta is located in the southern part of Mallorca Island (western Mediterranean). It was formed presumably by hypogenic processes in Upper Miocene reefal calcarenites. The cave hosts an important breeding colony of bats during the end of spring and early summer. Its microclimate is influenced by the presence of a thermal phreatic water table (27.7ºC) as well as by bat populations remaining in the cave along the reproductive season. The morphological bat-related features include bat claws and thumb marks scratches, together with several morphologies linked to bat excreta and aggressive leachates from guano. From the mineralogical point of view, this cave outstands regarding the presence of cave minerals linked to guano: nine phosphates have been identified, comprising three of them that are reported for the first time in Mallorcan caves (newberyite, struvite and whitlockite). Particularly interesting is the dichotomy between struvite and newberyite: the first one occurs when the cave is occupied by bat colonies (spring-summer), whereas in the colder seasons would occur the transformation of metastable struvite into a more stable newberyite. Caves with seasonal cyclical occupation of bat colonies could provide a new arena for the study of the guano-related mineral assemblages.