EVALUATING THE DECOMPOSTION OF MINERAL MUSEUM VIVIANITE SPECIMENS USING VISIBLE LIGHT, LONGWAVE UV LIGHT, AND HEAT EXPERIMENTS

Vivianite is a ferrous iron phosphate mineral (Fe^2+₃(PO₄)₂·8H₂O) that reacts with photons by converting water molecules into hydroxyl ion groups and oxidizing iron; however, the parameters of its decay are relatively unexplored. Therefore, the intention of this study is to explore causes and progressions of decay in a Bolivian vivianite sample and apply the results to JMU mineral museum vivianite specimens. Single crystals were exposed to laser light from an Ocean Optics IDRaman Micro Raman Microscope, UV light from a 6 Watt 365nm UV apparatus, and to a multi-step heating process using an Isotemp Fisher Scientific hot plate at 100°C. Additionally, these crystals were analyzed using a Thermo Nicolet iS50 FT-IR spectrometer. After exposing a Bolivian vivianite sample to incremental amounts of Raman light, longwave UV radiation, or heating, spectra were collected using Raman and FTIR-ATR spectroscopy. Additionally, spectra of single crystals of six museum specimens and ten micromounts were measured with the Raman and FTIR-ATR. Proceeding the Bolivian vivianite’s four separate exposures to Raman light, there was no visible alteration to the sample. Following exposure to UV light, new FTIR-ATR peaks appeared and increased in intensity the longer the sample was exposed but little change was detected with the Raman spectrometer. The heated samples showed changes in both the FTIR-ATR and Raman spectra, in addition to a notable optical color change. Some museum and micromount specimens showed spectra consistent with vivianite, some with metavivianite, and some with both depending on the apparatus used. While Raman light may not quickly affect a clear end member vivianite, a sample in a state of decay may experience damage. The development of FTIR-ATR intensity peaks indicate water molecules are being substituted by hydroxyl groups (Rothe et al., 2016). This suggests that low-frequency UV light has the capability of catalyzing the decay of vivianite to metavivianite quickly. Although the heat treated samples yielded altered FTIR-ATR and Raman spectra, more experiments are needed to understand the decay process. Using these conclusions, collectors, researchers, and museum curators can better understand how to protect and preserve vivianite specimens.