title: Iceland spar and its legacy in science
abstract: Abstract. In the late 17th century, Rasmus Bartholin and Christiaan Huygens investigated a curious optical property of crystals found at Helgustaðir in Eastern Iceland. This property which has been called double refraction, revealed in the 19th century a new aspect of light which turned out to be very useful as a probe of the internal structure of matter. Clear specimens of these crystals, an unusually pure variety of calcite, have since around 1780 been known as ''Iceland spar''. Few if any oth
journal: History of geo- and space sciences