High-temperature and “exotic” minerals from the Cioclovina Cave, Romania: a review

Bogdan P Onac, Herta S Effenberger, Radu C Breban

Research output: Contribution to journalArticlepeer-review

Abstract

This paper reports on the identification of four rare minerals in the phosphate deposit in Cioclovina Cave, Romania. Berlinite, AlPO4 and hydroxylellestadite, Ca5[(Si,P,S)O4]3(OH,F,Cl) are minerals that can form only at high temperatures, and would not be expected in a sedimentary environment. In this study we review the characteristics of berlinite and hydroxylellestadite from a heated sedimentary sequence in Cioclovina Cave (Romania) and refine their structure from single-crystal X-ray data. Two other minerals, churchite-(Y), YPO4⋅2H2O and foggite, CaAl(PO4)(OH)2⋅H2O are, for the first time, described from a cave environment. The minerals were documented by means of single-crystal X-ray investigations, X-ray powder diffraction, and electron-microprobe (EMPA) analyses. In addition, laboratory synthesis of berlinite was conducted and vibrational spectroscopy data were collected for hydroxylellestadite and churchite-(Y). Based on these investigations, we suggest that locally the heavily compacted phosphate-bearing clay sediments underwent a natural heating process. It is likely that in-situ bat guano combustion is responsible for generating the high-temperature environment needed for the genesis of berlinite and hydroxylellestadite. The occurrence of churchite-(Y) and foggite is related to guano-leaches that reacted with subjacent limestone and different allogenic cave sediments.

Original languageAmerican English
JournalDefault journal
DOIs
StatePublished - 1800

Keywords

  • cave minerals
  • guano combustion
  • Cioclovina Cave
  • Romania.

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