There are nine so-called cross stones (ristikivi) in the magic objects collection of the National Museum of Finland. One of these is a smooth, oval pebble with an inscribed cross on its surface. According to the museum catalogue, this one was kept in a pocket when venturing on a dangerous journey. The other eight stones are more or less roughly cross-shaped staurolite crystals.
Unfortunately, the catalogue does not give much information on the staurolites. One of them was owned by a cunning man from Iisalmi. There is no information how he might have used it or for what purpose. The other seven belonged to a set of objects in a birch bark container owned by a cunning woman in Suistamo. The catalogue mentions only that these have been used to heal boils and swellings on the skin. The same information is given for two “snake’s court stones” and one wooden gnarl in the same medicine box. This is a common use for the two latter types of objects, but the only case where staurolites are used similarly.
Staurolite crystals are widely known as magic objects. Sometimes they are called crosses of Coadry and used as charms against evil, such as several staurolites from France in the collections of the Pitt Rivers Museum of the University of Oxford. They may also be called fairy crosses. In their article Geology and the Dark Side, Christopher J. Duffin and Jane P. Davidson (2011) mention that one folklore explanation for the these crystals is that they are the petrified tears shed by fairies on hearing of the crucifixion of Christ. Ethnologist Auvo Hirsjärvi, who published the cross stones in the collection of the National Museum of Finland in 1965, also mentions that staurolites have sometimes been called stones of St. Peter or St. John. He adds that in Germany, these stones have protected against evil spirits and shock and they would heal fevers and bleeding.
Due to their curious natural shape, staurolites are still sold as souvenirs and amulets. In fact, as Hobart M. King notes in his online text about these minerals, “if you see a selection of these for sale that are all the same size, the same shape and containing gas bubbles, they might be manufactured”.
Archaeology of Folk Religion 