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    STUDIA GEOLOGIA - Issue no. 1 / 2004  
         
  Article:   VARISCITE (ALPO4Ľ2H2O) FROM CIOCLOVINA CAVE (ŞUREANU MOUNTAINS, ROMANIA): A TALE OF A MISSING PHOSPHATE.

Authors:  BOGDAN P. ONAC, J. KEARNS, RADU C. BREBAN, SIMONA CINT─é P├éNZARU.
 
       
         
  Abstract:  Recent investigations on a phosphatized sediment sequence in the Cioclovina Cave led to the identification of a second occurrence in Romania (first time in the cave environment) of variscite, AlPO4Ľ2H2O. The mineral exists as dull-white, tiny crusts and veinlets within the thick argillaceous material accumulated on the cave floor. Under scanning electron microscope (SEM) variscite appears as subhedral to euhedral micron-size crystals. The {111} pseudo-octahedral form is rather common. Variscite was further characterized by means of X-ray diffraction, thermal, vibrational FT-IR and FT-Raman spectroscopy, and by SEM energy-dispersive spectrometry (EDS). The calculated orthorhombic cell parameters are a = 9.823(4), b = 8.562(9), c = 9.620(5) ┼, and V = 809.167(6) ┼3. The ED spectrum of variscite shows well-resolved Al and P lines confirming thus the presence of the major elements in our compound. The formation of variscite is attributed to the reaction between the phosphate-rich leachates derived from guano and the underlying clay sediments.  
         
     
         
         
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