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.
Mottramite spreads in velvety green crusts that look like moss on rock. The soft coating is in fact a heavy lead-copper mineral carrying vanadium, the metal that toughens high-grade steel.
