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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