The importance of correct mineral identification for the determination of appropriate specimen storage conditions in geological museum collections

Many minerals are susceptible to environmental conditions; for example, several sulfates are prone to dehydration under low relative humidity. As such, the appropriate storage conditions required by minerals are species-specific. In an example presented here, stalactitic specimens previously thought to have been melanterite (a hydrated iron sulfate) from the South Wales Coalfield in the collections at National Museum Cardiff (NMC) were recently identified as being dominated by magnesium and aluminium sulfate species of various hydration states. The presence of epsomite in the majority of the analysed specimens indicates that it, rather than melanterite, was likely the initial predominant phase of the stalactites. Whilst the stability limits of hydrated iron sulfates markedly differ compared to those of magnesium and aluminium, all will dehydrate if stored under low relative humidity, as evidenced in the example provided here. Specimen storage in fluctuating and low relative humidity environments resulted in the dehydration of the magnesium and aluminium sulfates to lesser hydrated sulfates, and consequently resulted in partial loss of the original specimens. As storage environments affect long-term preservation and appropriate storage conditions for minerals are species-specific, the accurate identification of mineral specimens is imperative for the determination of appropriate storage conditions.