The ship sank in 1592. Scientists say they believe the substance made of calcite and known as Iceland xpar, was used as a navigational tool alongside the compass. This tracks with ancient Norse mentions of such a tool, which probably existed as well.
There have been references to the magic crystal in Norse literature, such as the Sagas of Icelanders, but no evidence had been found at Viking burial sites—most likely due to the practice of cremating the warriors, which would have destroyed the crystals.
Source: Yahoo News: Claudine Zap