Did you know?
Look through a clear rhomb of Iceland spar calcite and the world doubles, split into twin images by the crystal's double refraction. Some researchers think Norse sailors used this very effect to find the sun through cloud, the so-called sunstone, though the idea remains a debated hypothesis.
Fluorite gave fluorescence its name. In 1852 the physicist George Stokes, studying the mineral's glow under invisible light, coined the word for the whole phenomenon after the stone itself.
