A mineral that changed science. The clear calcite from the Helgustadir mine in eastern Iceland splits a single image into two (double refraction), and it was the stone Bartholin, Huygens and Newton argued over, the material that revealed the polarisation of light, and it is claimed as the Viking “sunstone” used to find the sun through cloud. The mine is a PROTECTED natural monument now; collecting is prohibited, but you can walk it.
Optical calcite (Iceland spar)
Iceland
See it on the map
Other places on the map within a couple of hours.
