Revisiting three minerals from Cioclovina Cave (Romania)

Cioclovina Cave in Romania’s Southern Carpathians is a world-renowned cave site for its paleontological, anthropological, and mineralogical (type locality of ardealite) findings. To date, over 25 mineral species have been documented, some unusual for a cave environment. This paper presents details on the occurrence of collinsite [Ca2(Mg,Fe2+)(PO4)2·2H2O], atacamite [Cu22+Cl(OH)3], and kröhnkite [Na2Cu2+(SO4)2·2H2O] based on single-crystal X-ray diffraction, electron microprobe, stable isotope analyses, and scanning electron microscope imaging. This is the first reported occurrence of kröhnkite in a cave environment. Atacamite represents the weathering product (in the presence of Lower-Cretaceous limestone-derived chlorine) of copper minerals washed into the cave from nearby ore bodies. Atacamite, and kröhnkite have similar sources for copper and chlorine, whereas sodium probably originates from weathered Precambrian and Permian detrital rocks. Collinsite is believed to have precipitated from bat guano in a damp, near-neutral pH environment. The results show the following sequence of precipitation: ardealite-brushite-(gypsum)-atacamite-kröhnkite. This suggests that the observed mineral paragenesis is controlled by the neutralization potential of the host-rock mineralogy and the concentrations of Ca, Cl, Cu, and Na