Remember the blog post I did about sun stones and Viking navigation? Two years ago? No? You haven't memorized the blog yet??
Well, short version then. Or, y'know, hit the link.
In the North Atlantic, in the middle ages, there are references, in different texts, about "sun stones" being used, primarily by Vikings, to navigate. Up there, that far north, navigating by star in the summer is pretty tricky, since the sun doesn't always go down. According to various accounts, sun stones would allow a person to find the direction of the sun, even on cloudy days.
Scholars have speculated for many years about what exactly a sun stone was. Or claimed it was crap, because what could ancient man know that fantastically wonderful history PhDs don't? (I could fill several books.) But, the big question has always been, if it was legit, what in heck kind of stone was it?
Over the last decade or so, they have found big, clear hunks of calcite in ship wrecks, and someone figured out how to use them to, hey, tell which direction the sun is on a cloudy day. Most people said question answered, snooty idiots claimed there wasn't enough evidence.
They found another piece of calcite in another ship wreck, announced this week. Take that, sneering ethnocentrist ivory tower knuckleheads.