Revisiting three minerals from Cioclovina Cave (Romania)

Abstract

Cioclovina Cave in Romania’s Southern Carpathians is a world-renowned cave site for its paleontological, anthropological, andmineralogical (type locality of ardealite) finds. To date, over 25 mineral species have been documented, some unusual for a caveenvironment. This paper presents details on the occurrence of collinsite [Ca2(Mg,Fe2+)(PO4)2·2H2O], atacamite [Cu22+Cl(OH)3], andkröhnkite [Na2Cu2+(SO4)2·2H2O] based on single-crystal X-ray diffraction, electron microprobe, stable isotope analyses, and scanningelectron microscope imaging. This is the first reported occurrence of kröhnkite in a cave environment. Atacamite representsthe weathering product (in the presence of Lower-Cretaceous limestone-derived chlorine) of copper minerals washed into the cavefrom nearby ore bodies. Atacamite and kröhnkite have similar sources for copper and chlorine, whereas sodium probably originatesfrom weathered Precambrian and Permian detrital rocks. Collinsite is believed to have precipitated from bat guano in a damp, nearneutralpH 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 theconcentrations of Ca, Cl, Cu, and Na.

Keywords

• cave minerals
• sulfates
• phosphates
• guano
• stable isotopes
• Cioclovina Cave
• Romania