Not ordinary sand. Black grains along Iceland's exposed shore come from lava-born basalt, not the quartz-rich debris common on pale coasts, as eruptions, cooling, and erosion reduce volcanic rock into a dense cover beneath the surf. The color persists.The beach is a grinder, not a pigment trick. Physics does the work. Basalt erupts as magma, cools into fine-grained igneous rock, and breaks under t...More