A sunstone, used by mariners to judge the position of the Sun when it is cloudy, has been found at a 16th century shipwreck.

A previous study showed that calcite crystals reveal the patterns of polarized light around the sun and, therefore, could have been used to determine its position in the sky even on cloudy days. That led researchers to believe these crystals, which are commonly found in Iceland and other parts of Scandinavia, might have been the powerful “sunstones” referred to in Norse legends, but they had no archaeological evidence to support their hypothesis—until now.