Possibility of Huntite presence in the Triassic limestones of Opole Silesia

This article presents the results of studies of Triassic carbonate rock samples taken from the area of Opole Silesia. The aim of the study was the identification of a huntite-carbonate phase characterized by a higher content of magnesium in comparison with magnesium calcite and dolomite. Huntite is usually fomied during hydrothermal processes or weathering of dolomite. It could be also a product of magnesium calcite transformation under high temperatures. In sedimentary rocks, this mineral occurs in deposits of the vadose-water zone. Selected rock samples were examined using FTIR spectrometry. X-ray diffraction, and microprobe me- asurements. Huntite was identified in Muschelkalk rocks, in the limestones of the Gogolin Beds, Górażdże Beds, Dziewkowice Beds, and Karchowice Beds. Results of FTIR spectrometry showed that in the infrared absorption curves of the analyzed samples, there occurred an absorption band of 1555 cm-1 in samples 1 and 4, in sample 3 an absorption band of 1562 cm-1, and in sample 2 an absorption band of 1572 cm-1. These absorption bands are typical for huntite. In X-ray diffraction patterns, carbonate phase treated as huntite was identified on the basis of a diffraction line which presented the highest intensity and d^i value - 2.83 A. Results of microprobe measurements delivered extensive information. This method allowed for the identification of huntite in limestones of the Dziewkowice and Karchowice Beds. The amounts of magnesium determined in selected points of the examined samples varied from 14.01% Mg (23.23% MgO) to 16.18% Mg (26.83% MgO). These values are higher than magnesium values typical for Mg-calcite. They also exceed the stoichiometric value typical for dolomite (21.86% MgO, 13.12% Mg). The content of Mg measured for huntite in the points of the microareas is lower than the stoichiometric value for this carbonate phase (20.65% Mg, 34.25% MgO). The reduction in magnesium ions could be the effect of diagenetic processes (dedolomitization?). Analyzing the possibilities of huntite formation, the carbonate phase characterized by an amount of mag- nesium higher than in Mg-calcite and dolomite, it can be hypothesized that this mineral was fomied in areas of the Germanic Basin where diagenetic processeswere occurring with the contribution of waters of the vadosezone.