https://www.livescience.com/16831-viking-sunstone-crystal-compass.html
'Magic' Viking Sunstone Just Natural Crystal | Live Science
Nov 2, 2011 - A common Iceland spar (a translucent crystal formation of calcite) can behave like the mythical sunstone by depolarizing the light from the sun to reveal its...
viking sunstonejust naturalmagiccrystallive
https://theweek.com/articles/466806/did-scientists-just-find-fabled-viking-sunstone
Did scientists just find the fabled Viking sunstone? | The Week
Jan 8, 2015 - The mythical rock was said to help ancient sailors navigate the seven seas
find theviking sunstonescientistsfabledweek