Comparative Raman Spectroscopic Analysis of Slavíkite From Its Type Locality and Other Occurrences

Slavíkite, (H 3 O + ) 3 Mg 6 Fe 15 (SO 4 ) 21 (OH) 18 · 98H 2 O, is a rare and structurally complex secondary sulfate occurring in sulfide‐weathering zones and acid mine drainage environments. We present a detailed vibrational spectroscopic study of slavíkite from its type locality at Valachov Hill and two additional occurrences in the Czech Republic using Raman spectroscopy, complemented by Fourier‐transform infrared spectroscopy, powder X‐ray diffraction, and electron probe microanalysis. Raman spectra are characterized by three intense bands in the sulfate ν ₁ stretching region at 988, 1010, and 1033 cm −1 . A pronounced orientation dependence of Raman band intensities was identified as a critical factor affecting spectral interpretation and potentially leading to the misidentification of slavíkite as mixed sulfate assemblages. Despite minor Al substitution detected in all studied samples, Raman and FTIR spectra from different localities and specimens collected over a period of nearly four decades show only negligible differences, indicating long‐term preservation of the mineral structure under ambient conditions. Thermo‐Raman experiments reveal stability up to ~60°C, followed by progressive dehydration and structural collapse above 70°C, completing above ~330°C. Heating to 600°C results in the formation of stable products of hematite and anhydrous Mg‐sulfates. The dataset provides a robust reference for slavíkite identification and improves understanding of its structural stability and transformation pathways in complex sulfate assemblages.