In 1592, a British ship sank near the island of Alderney in the English Channel carrying an odd piece of cargo: a small, angular crystal. Though cloudy and scuffed up from 4 centuries at the bottom of the sea, its precise geometry and proximity to the ship's navigation equipment caught the eye of a diver exploring the wreckage. Once it was brought back to land, a few European scientists began to suspect the mysterious object might be a calcite crystal, which they believe Vikings and other European seafarers used to navigate before the introduction of the magnetic compass. 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. After subjecting it to a battery of mechanical and chemical tests, the team determined that the Alderman crystal is indeed a calcite and, therefore, could have been the ship's optical compass, they report online today in the Proceedings of the Royal Society A. Today, similar calcite crystals are used by astronomers to analyze the atmospheres of exoplanets—perhaps setting the stage for a whole new age of exploration.
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