Vitriols, known today as sulfates of divalent metals, played an important role in the development of modern chemical and metallurgical practice, and engaged the speculation of alchemists and mineralogists. The natural occurrence of vitriol and its earliest recognition as a distinct group of related minerals is discussed. The unique position of vitriol was codified in al-Razi's (854 - 925/935 AD) classification of mineral substances. On the contrary, although considered to be a noteworthy mineral substance in Indian alchemy, vitriol is not recognized as a distinct mineral, the blue and green varieties being classed separately according to other criteria. The deposition of Cu from a vitriol solution on an iron surface was known in some ancient cultures, and it became even used on an industrial scale in the 11th and 12th centuries AD. These reactions, which were sometimes construed as an apparent transmutation of metals, were further investigated and were significant for European alchemy and mineralogy. The practice of preparation of nitric acid from vitriol, which seems to have begun around 1300, soon increased the number of known chemical reactions. Aqua regia was a further innovation that made possible the dissolution of gold, which had previously been considered as the indestructible metal. Particular attention is paid to the preparation of sulfuric acid from vitriol. Several descriptions of a red solution obtained during this process lead to the consideration of a process from the Summa Perfectionis of Pseudo-Geber that could have resulted in sulfuric acid, and in which contamination with Se could have led to the red product.