The remains of the world’s largest spar quarry lie east of Eskifjörður. Iceland spar (silfurberg in Icelandic) is a type of calcite crystal that is completely transparent and can split light into two parallel beams. It was a vital component in early microscopes.
To reach the quarry, follow the gravel road past Mjóeyri, driving 7km along the coastline until you reach an information panel and public toilet; the quarry is then a 500m walk uphill.
Large quantities of Iceland spar were exported to Europe’s top scientists from the 17th century until the quarry's closure in 1924. The largest specimen taken from Helgustaðanáma weighs 220kg and is displayed in the British Natural History Museum.
Science aside, you can still see calcite sparkling in rocks around the quarry. The area is a national preserve, so it is absolutely prohibited to poke out pieces of crystal or take them away.