Sólarsteinninn. Tæki eða tákn?
Two 13th-century narrative sources from Iceland, Rauðúlfs þáttur and Hrafns saga Sveinbjarnarsonar, mention the sunstone (sólarsteinn), a mineral by which the sun could be located in overcast sky. Sunstones are also mentioned in church and cloister inventories (14th–15th century) without discussing their attributes. The Danish archaeologist Thorkild Ramskou pointed out that the sunstone could have been one of the minerals (probably chordierite) that polarize light and by which the azimut of the sun can be determined in a partly overcast sky or when the sun is just below the horizon. The principle is used by many animals and was applied during polar flights before more advanced techniques became available. No other records of the sunstone exist in medieval literature. Ramskou’s theory that the sunstone could have aided navigation in the open sea in the Viking period has become very popular. Used singly, however, a polarizing mineral only gives the horizontal angle of the sun (azimut) and does not help much when navigating the open sea. The problem with two of the sources is that they are allegorical. Hrafns saga contains a burst of purely allegorical material associated with Hrafn’s slaying. This involves a celestial vision with three highly cosmological knights, recalling the horsemen of the Apocalypse. The horsemen of Hrafns saga contain allegorical allusions to the winter solstice and the four elements as a foreboding of Hrafn’s death. Rauðúlfs þáttur, a short story about Saint Olav, is the only source mentioning how the sunstone was used. Rauðúlfs þáttur is, however, a thoroughly allegorical work. A round and rotating house visited by Olav seems to be a model of the cosmos and the human soul, as well as a prefiguration of the Church. The purpose of the author seems to be the apotheosis of St Olav, and this is achieved by placing him in the symbolic seat of Christ. The house belongs to the genre of “abodes of the sun” which were widespread in medieval literature. St Olav employed the sunstone right after leaving this allegorical house. It is conceivable that in Rauðúlfs þáttur the sunstone was used as a symbol of the Virgin, following a widespread tradition where her virgin birth of Christ is compared with glass letting a ray of the sun through. Despite the allegorical nature of the above mentioned sources the medieval church and cloister inventories show that sunstones existed as physical objects. Furthermore, the deciphering of the allegory in Rauðúlfs þáttur does not expose the sunstone as wholly fictious, although its presence in the story may be entirely symbolic. Its use is described in enough detail to show that the idea of using a stone to find the position of the sun in overcast conditions was currently around. The idea was later shown to be well founded when polarizing minerals were (re)- discovered. A polarizing crystal would have been useful as a sundial, especially at high latitudes with extended hours of twilight or in mountainous areas or in partly overcast conditions, but only in conjunction with known landmarks. Churches and cloisters would have valued such an object as an aid to keep track of the canonical hours.